Hey Guys,
My garage has a 60 amp subpanel with fuses that I’m just about ready to outgrow. Since I’m in the planning stages of the upgrade, I’m wondering if some of BT’s might be able to shed a little light on my situation.
First, I’ll be replacing the cable between my house and garage. A friend works for an electrical contractor and can get me a lenght of whatever size cable I need. I’ve not been able to find a straight answer on what size that might be.. I’m thinking my subpanel needs to be 100amps. Also, what’s the best practice to strip the wires for a cable this large?
Second, I assume that since my garage is detached, I’ll need a seperate ground rod to meet code. The garage currently does not have one. I’ve never driven a ground rod before, is this a big project?
Third, I’m getting a Mini-max CU300 5-1 Combo machine (woodworking) that needs one 30 amp 220 circuit. However, in the meantime, I’d like to convert my other machines to 220. Where might I find the formula for how many circuits can be added on a 100amp subpanel?
I’m not opposed to hiring a pro if this gets to big, just trying to evaluate the size of the project.
Thanks!
Patrick
Replies
My inspector required 2 grounding rods, 6' apart. I hand drove them, not a good idea. An attachment for an impact driver is the way to go.
Think I would use a rotary hammer not impact driver, think that is what you might have meant. A piece of pipe with a cap will do it manually in a pinch.
Patrick - Since I've been through a similar situation I'll get the ball rolling on this and then bow out to the true electrical guys here.
First of all, you've got some homework to do. I'm guessing based on what you wrote, but it sounds like you've got a 60 amp breaker off your main panel going to a subpanel in the garage with fuses. If so, you need to know:
1) What size service is your main panel......100 amp or 200 amp?
2) What's the current load on your main panel? If you're already close to using 80% or more of your capacity you might not have room to add a bigger subpanel in the garage.
3) What's the current load on your 60 amp subpanel in the garage? I don't know what else you might have out there (water heater?, dryer?) but if you're just a one-man shop you might not NEED bigger than a 60 amp service out there. If that's the case, you might not need to replace the wire run from the main panel...just replace the subpanel.
4) The max amount of load that you're planning to be able to run at one time on a subpanel should be no more than 80% of the breaker you use on the main panel....a 60 amp breaker controlling a subpanel should have no more than 48 amps running at once. Once that's determined, the breaker size along with the length of the wire run between the main panel and subpanel determines the wire gauge to use for the run. So you also need to know how far it is from the main panel to the subpanel. I'll let the 'lectrical guys continue that thought.
5) The subpanel itself can handle as many circuits as there are spaces for them on the subpanel....but if you keep adding high amp loads and try running them at the same time you're gonna trip a breaker. The breaker is there to protect the wire from self destructing.
6) Yeah, you need a grounding rod or rods....it differs depending on where you live as to how you do it. Just make sure you know where all your water/gas pipes, etc are before you start driving them. Since your garage is detached you also need to isolate the neutral bus bar from the grounding bus bar in the subpanel. Again, I'll let the 'lectrical guys elaborate.
7) Finally, if it helps any, most one man shop guys and/or hobbyists do all the research and end up with 60 amp subpanels coming off of their main service. This is usually more than adequate if you're the only one out there running the machines. And if that's your situation, you might save a lot of time by just replacing the fuse panel with a breaker panel.
Hope the above helps.
charlie -- "Count your blessings....it could always be worse!"
Edited 7/9/2007 8:44 pm by charlie4444
Edited 7/9/2007 8:45 pm by charlie4444
"6) Yeah, you need a grounding rod or rods....it differs depending on where you live as to how you do it. Just make sure you know where all your water/gas pipes, etc are before you start driving them. Since your garage is detached you also need to isolate the neutral bus bar from the grounding bus bar in the subpanel. Again, I'll let the 'lectrical guys elaborate."With a detached garage you have the two options.One is what you say run a separate EGC (ground) and neutral. Unbond the neutral in the panel and, if needed as a ground bus bar kit. This is the most universal method.It is also what is need for a sub-panel in the same structure as the service disconnect (ie, main panel).But if there are no other metalic connections between the 2 structures, such as water pipe, gas pipe, phone line, or cable then you have the option of only running a 3 wire, 2 hots and a neutral. And treating the panel as a serice entrance with the neutral bonded to the ground.In any case a ground electrode system (ground rods or other electrodes) is need at the separate structure.For sizing you need to look at the largest combination of equipement that might be running at any one time.In the OP case it is most likely the Mini-Max, dust collector, light, and heat or AC.Use the actual nameplate data o fthe equipment. NOT the circuit rating.Most likely 60 amp is more than enouh. And with the cost of wire you might want to use.But I still recommend getting a 100 amp panel. 100 amp is a very common size and thus you can get inexpensive ones with LOTS of spaces for breakers..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
> I've never driven a ground rod before, is this a big project?
It can be, but there are ways to keep it simple. The first thing to remember is that, if the building has a real foundation, the ground near it will have been disturbed by the backhoe (or whatever dug the trench). Driving your rod within 12" of the footing will be easier than further out. In addition, I waited until we got about 3 days of steady rain. When the rain quit, I was out the door with a sledge hammer.
> Where might I find the formula for how many circuits can be added
> on a 100amp subpanel?
You don't really need one. Just figure out how much power you will pull maximum. For example, my shop has two 15 amp 220 lines and two 20 amp 110 lines. My dust collector pulls 4 amps (220) when running, and my table saw pulls a bit over 8 amps on startup. Total would be 12 amps if I'm using that tool. Alternately, I could be using the radial arm saw, which pulls 14 amps (110). That would be a total on one leg of around 18 amps.
I've looked at other combinations, but the gist of it is that there is just about no way that I'm going to be using more than 20 amps at any one time. My subpanel is on a 30 amp breaker, and that's overkill.
So. You figure out how much power you could possibly use at one time and divide that by .8. That's your minimum main breaker size. The number of circuits allowed is whatever you want to have. Working backwards, you can use 80 amps on a regular basis with a 100 amp main. That could be 2 circuits or 200, your choice.
I have driven several. It generally takes luck, patience, and a reasonably strong arm (or even more patience). I have driven them with a fence post drive that is made for driving "T" posts. It is simply a piece of 2" steel pipe with a cap welded on. Some have handles, but not totally necessary. You can get them at any farm supply store and possibly at some of the big boxes. A couple of years ago they were around $20 - don't know the current price.
I have driven them in completely with a 2lb sledge. Unless the ground is soft, the top of the rod can mushroom out quite a bit. The last one I drove, I took a 3/4" pipe nipple and put a threaded cap on it and then put that over the top of the rod and beat on that. Unfortunately, the steel in the cap fatigued and the rod came right through the top, so I got another cap and then put a heavy duty washer inside and that absorbed enough of the shock to get the thing in the ground.
A rotary hammer might be the way to go, I don't know if the top the rod would bugger up the drive shoe inside the rotary hammer, however. You could get a cheap rotary hammer on sale at Harbor Freight (I got one for $69) so you wouldn't have to worry that much about messing it up.
They make special drivers to attach to Hole Hawg (or similar) heavy duty drills, but that would be for someone who installed a lot of them.
Some people have suggested using a water hose to wash out a hole for the ground rod. I think that would be a very bad idea in that the resulting hole probably would not fit tight enough around the rod to give low resistance to the ground.
If you can't drive it in far enough, there are other alternatives to the vertical ground rod.
Have fun, and have some pain reliever handy for the sore triceps and shoulder if you pound it in with a sledge...
Thanks for the responses so far, guys!
My main panel is 200amps and I have six spaces left. I haven't figured out the exact amp draw, but I have lots of extra circuits that go unused most of the time. So, as a rough guess, I think 100amps should be fine for a subpanel. However, I'd like to verify that for sure. Is there a formula to use?
I'm amazed at the amount of what appears to be incorrect information on the Internet about this subject. Especially in regards to cable sizing and need for ground rods.
From what I can tell for 100amps, the underground cable should be at least a 4, but maybe a 2 would be preferred? I'm going about 45 feet from the panel to the garage.
Second, the garage currently does not have any ground rods and the fuse panel appears to me to be a mess (more than one wire under panel screws, etc). I also have an issue with what I think is a floating neutral (1 or 2 volts even when circuit is turned off). Could this be traced to lack of ground rods?
Can someone enlighten me on the theory behind why ground rods are needed with a separate structure? Where ground rods not required in this application 20 years ago? I fully intend on installing them when I do the panel, just curious to know how they work.
Second, am I going to be struck down with the panel and ground issue the way they are? The wiring is all in good shape and the panel is not overloaded, just looks like poor workmanship. With the investment in my new machine, I want to make there are no issues.
Thanks for all the help!
Patrick
Edited 7/10/2007 2:33 pm ET by Corrib
<<Second, am I going to be struck down with the panel and ground issue the way they are? The wiring is all in good shape and the panel is not overloaded, just looks like poor workmanship. With the investment in my new machine, I want to make there are no issues.
Not sure what you mean by that.
You are completly removing the old 60 amp fuse box when you put in the new 100 amp sub panel aren't you? You can straighten out all the circuite issues in the new panel, so what the oldbox looked like won't make any difference.
#4 is fine for a 100 amp panel unless you are over 100 feet from the main panel in the house. You can use #6 from the new panel to the ground rods. Be sure to strip it or tape it with green tape.
Since you are going underground. my preferenc is to use PVC conduit and pull in the wire. It is a safer install IMO. You are futer owners of the home are less apt to damage conduit than u/g cable when doing gardening or something in the future.
Dave
"For sizing you need to look at the largest combination of equipement that might be running at any one time.In the OP case it is most likely the Mini-Max, dust collector, light, and heat or AC.Use the actual nameplate data o fthe equipment. NOT the circuit rating.Most likely 60 amp is more than enouh. And with the cost of wire you might want to use.But I still recommend getting a 100 amp panel. 100 amp is a very common size and thus you can get inexpensive ones with LOTS of spaces for breakers.""I also have an issue with what I think is a floating neutral (1 or 2 volts even when circuit is turned off). Could this be traced to lack of ground rods?"What are you measuring between? "Can someone enlighten me on the theory behind why ground rods are needed with a separate structure?"There are 2 reason for ground rods. One is to reference the local grounds to the earth. You don't want to set out of the building and have some metal that is "grounded" to the buildin's ground, but have the whole building floating at a high voltage. If there where no ground rods on the system at all you can get thousand of voltage with reference to the earth. But the ground electrodes(if the connection is not damaged) will take care of that. But you can still get a small difference. Typically not enough to notice. But for things like pools it can be a real problem.The other purpose is a discharge for lighting scriks. And you can sill get large voltages induced in the circuit."Second, am I going to be struck down with the panel and ground issue the way they are? " I don't understand the question?"From what I can tell for 100amps, the underground cable should be at least a 4, but maybe a 2 would be preferred? I'm going about 45 feet from the panel to the garage."Code requires #3 CU assuming that the wiring and terminals are raded for 75C, which it should be in most cases.#4 is only allowed for feeders for DEWELLING UNITS. That is becaused residential useage variaies a lot and 90% of the time will be much less.Codes does not have any special provisions for things like a residential shop that is overwired in the first place..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks for the info about the grounds and my various other questions.
In regards to the "struck down" portion of my last post, I was trying to make a bad joke about the the fuse panel. I should stay away from humor..
Joking aside, what I meant to say was, is the fuse panel dangerous with multiple wires under one screw and no ground rods? And, is there an issue with my upcoming Mini-Max purchase (with its European-made motors) by using with the fuses as they are?
The voltage reading was with my multi-meter between the hot and neturals on a 120 circuit. Probably one or two volts as I remember. It happens on all of the 120 circuits in the garage (I haven't checked the one 220)
Thanks again for all the info!!!!
Patrick
Edited 7/10/2007 3:20 pm ET by Corrib
"Joking aside, what I meant to say was, is the fuse panel dangerous with multiple wires under one screw and no ground rods? And, is there an issue with my upcoming Mini-Max purchase (with its European-made motors) by using with the fuses as they are?"Dangerous is relative.First, but not least is the danger when the wife sees the check for the Mini-Max <G>.The lack of grounding rods does not meet current codes, but it is not a serious problem and would be just as safe or unsafe with the MM as with your current equipment.The multiple wires under a screw is a more serious problem. A perfect place for poor connections, thus heating arcing, smoke and other problems.If it was me I would go ahead and install a 100 amp sub. You can upgrade the feeder and ground rods later.Also I suspect that the existing system might be 3 wire and the neutral bonded to the ground.See this message about 3 wire vs, 4 wire.
http://forums.taunton.com/tp-breaktime/messages?msg=92116.5And some places require 4 wire for all detached buildings.But in any case I would assume that you need to so that ground bus kit, if needed. And keep the neutrals on the neutral bus and the grounds on the ground bus..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill,
As always, thanks! I especially appreciate the info about the 3 verus 4 wire stuff.
In addition to the electrical knowledge, you've hit the nail on the head about my tool purchase.
A mild electrical shock might be more pleasant than her inquiring about the giant white machine in our garage. "Oh, that? I've always had that, it's not new.".... ;)
Patrick
"A mild electrical shock might be more pleasant than her inquiring about the giant white machine in our garage. "Oh, that? I've always had that, it's not new.".... ;)"Perfect solution.Just have them ship it to me.After I use for a year or two then it will be clear used and she won't even notice it..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Patrick - I'm starting to think that you really should hire an electrician, but let me try clarifying some stuff.
1) "My main panel is 200amps and I have six spaces left. I think 100amps should be fine for a subpanel. " I'm not sure you realize that we are talking about 2 different things here: the size of the circuit breaker on your main service panel that will control the subpanel; and the rated size of the subpanel that you'll buy. We're telling you to get a subpanel that is rated for 100amps...they're common and relatively inexpensive. BUT THAT DOESN'T MEAN you need to set it up as if you're going to utilize the full 100 amp capacity of it by running it off of a 100 amp breaker on your main service panel. That's huge overkill. If you already have a subpanel controlled by a 60 amp breaker on your main WHY NOT LEAVE IT AS IS and just change out your subpanel?
2) "Second, am I going to be struck down with the panel and ground issue the way they are?" You're talking about getting shocked, right? If you don't feel knowledgeable or comfortable enough to be able to stay safe around the wires I really recommend you having an electrician do it. The overall process you'd have to do if you follow all our advice is:
a) Turn off the power at the main service panel.
b) Disconnect the old fuse subpanel from the main panel.
c) Connect the new 100 amp subpanel to the main service panel.
d) Transfer all the garage circuits from the old subpanel to the new.
e) Install grounding rod(s).
f) Turn on the power at the main service panel.
You have to understand that the National Electrical Code has changed numerous times over the years based on what is agreed upon as the safest way to go. These are supposed to be caught up to date when houses are bought and sold but that doesn't always happen. We used to all drive around without seatbelts......times change.
charlie -- "Count your blessings....it could always be worse!"
Edited 7/10/2007 5:11 pm by charlie4444
I think I did a poor job of wording here. There are actually two seperate issues here.
Your idea of just replacing the fuse panel instead of the whole system is a good one. But 60 amps would appear to be only the minimum requirements for machine (4.8hp motors, not sure about exact amp draw, says they need a 30amp circuit), dust collector (8 amps), and lights (5-ish). Even though I'm fairly sure the machine isn't always drawing 30, I don't think 17 amps would be enough for electric heat in the winter. In which case, does it make sense to go to 80 or 100 amps on the breaker side?
What I was referring with the fuses is a seperate issue. I'm not familiar at all with fuse panels and one of this vintage (back when they wrote with quills, apparently) really concerns me. I don't think I would get shocked by it in use, but I am concerned about overall safety and having more than one wire under each terminal screw on the fuse panel.
My own heartbeat aside, potential motor issues on my upcoming 5 in 1 combo machine purchase have made me decide the fuses need to go away.
Thank you for helping me think "outside the box"...
Edited 7/10/2007 5:43 pm ET by Corrib
No prob. FYI - If your MM 4.8hp motor says it needs a 30 amp circuit then that means it's drawing no more than 24 amps when running (the 80% rule again). For that amount of horsepower on a 240v circuit I would guess it's really drawing around 17 to 18 amps most of the time.....too much for a 20 amp circuit but well within a 30 amp circuit (which is why it says it needs 30amp). You're now up to 30+ amps total for the lights, DC, and MM. That leaves around 18 amps for heating (staying within the 80% rule for the existing 60 amp circuit). For a typical garage your heater's going to run around 15-20 amps at 240v for 13,000-17,000 BTU's....which all appears to work quite nicely if your garage is no bigger than, say, 400 sq feet.
But hey, if you want to spend serious money on copper at today's rates go for it. I can understand the wish for future expansion room. Whatever you do I'm definitely with the earlier suggestion that no matter what switch out the fuse panel with a 100 amp subpanel NOW.charlie -- "Count your blessings....it could always be worse!"
You're still getting some mis-information here. There is no 80% rule about the breakers, except for the resistance heating load.
So you have a dust-collector drawing 8 amps. At120v or 240v? Big difference in wattage, i.e. 960W or 1,920W. And the lights: 5 amps of 120v or 240v? Again, different.
That's why I suggested you figure it in WATTS. You add your wattage totals and divide by 240v to get the total amp load.
When installing a motor circuit we are required generally to size it according to a table in the NEC (430.148) regardless of the value on the motor plate. There is no listing for 4.8 hp so I looked at 5 hp. A 5-hp motor at 230v will draw about 28amps. This would need #10 wire and minimum 30a breaker and you would figure roughly 6,700 W running load.
So, total the wattage. For resistance heating you should figure the load in watts and add 25%. Divide by 240. There's your minimum main breaker or fuse size. And that of course determines your wire size.
Ed
Edited 7/11/2007 5:18 am ET by edlee
You're still getting some mis-information here. There is no 80% rule about the breakers, except for the resistance heating load
Glad you said that.
How old is an "old electrician" ?
Dave
Based on the wattage calculation, it would appear that my current 60 amp setup would be more than enough. So, I might so replace the fuse panel with breakers.
6,700w for Mini-Max
1,000w for dust collection
1,000w for lights (200w bulbs)
However, adding the 6,000w heater puts the amp calculation about 61.25. So, I think I'll have to consider if having electric heat is worth adding the upgraded breaker and feeder cable.
Two final questions, and I'll call this thread complete.
Does the 5hp motor need a motor starting fuse at the receptacle?
Is there any easy way (other than digging up my yard) to find out whether I have conduit between my main panel and garage currently?
Thanks again! You guys have been helpful as always!
Patrick
Truly sorry about the mis-info guys. Glad you other guys were there to straighten me up. Got lazy and didn't calculate in watts which as you saw was a big mistake.
Patrick - good luck with the wiring! Sounds like you've got a handle on exactly what you're dealing with now.charlie -- "Count your blessings....it could always be worse!"
>Two final questions, and I'll call this thread complete.
You obviously don't understand this forum . . .
Once you start a thread, it has a life of its own, and it can take whatever twisty-turny path it wants to :)
Don
Does the 5hp motor need a motor starting fuse at the receptacle?
Sorry, I don't understand the question. A 5-horse motor needs a starter with overloads unless there's built-in thermal protection. But you don't necessarily need additional fuses to supplement the branch-circuit breaker...if you do it would be in the manufacturor's spec's. Does that answer your question?
Is there any easy way (other than digging up my yard) to find out whether I have conduit between my main panel and garage currently?
Well, what type of wire is it? UF or individual conductors?
Ed
I think 100amps should be fine for a subpanel. However, I'd like to verify that for sure. Is there a formula to use?
There's no 1-size-fits-all formula. I think someone already said something like this, but figure out in watts how much power you might use simultaneously.
500 watts of lighting, a mini-fridge and a tablesaw? I just made that up, but it's to give you an example. So the mini-fridge only draws power (maybe 4amps , 500W)when the compressor is running, like 10 minutes in an hour; the table saw motor, say it's 1-1/2 hp draws maybe 10amps @ 240v (2,400W) when it's running, which could be for a 30-second cut or 1/2 hr. for a series of cuts; and the lights will be on most of the time you're working. So, if you look at that you see that you don't really need much to power those 3 applications. 100amps = 24,000W (theoretically).
I'm amazed at the amount of what appears to be incorrect information on the Internet about this subject. Especially in regards to cable sizing and need for ground rods.
Well there are a lot of people who's experience is limited and or have opinions based on how they've seen it done in their neck of the woods, or pick something up from one inspector and think that that is the way it has to be. And then even amongst electricians there is a lot of debate about a lot of things.
Grounding is often a tricky issue, though this question of 3 wires or 4 is one of the most commonly discussed on boards like this (I don't think there's much debate about this amongst electricians, it's somewhat subtle when to use 3 or 4 but it's pretty clear). The wire size can be tricky too. Bill Hartmann gave you the correct answer, #3 if you're using copper and 75-degree terminations(#1 for aluminum).
#4 for 100amps is a special application that doesn't apply in this case.
Ed
I've got a similar situation, but the building is the third of three, so I'm adding another grounding rod. That way, for only $14, I don't have to buy the heavy copper grounding wire and run the 4th wire with the #3 size 220v wiring. The original problem I faced with the first building was trying to drive a grounding rod into 6" of topsoil and a 2' thick layer of ROCK.
The electric company said I could drive the ground rod horizonally under the slab and into the damp sand and soil. Hammering sideways was a chore, but I had no other choice and it's worked fine the last 12 years. I chose to use the 5/8" copper coated grounding rod. For only $4 more than the cost of the 1/2" size, it was easier to drive and gives a little more surface area to contact the damp soil.
I would remind you to be sure to put the bonding collar before you start driving the end of the grounding rod. The end will mushroom and you'll have to hacksaw it off to get the collar to slide on....
Bill
Corib,
My 100 amp breaker box is full, and yet I ran into a problem.
I do arc welding outside the workshop, so I as I built the workshop, I had wired a220v, 50 amp plug on a wall near the door. I came up with a 3hp jointer that requires only a 30 amp circuit. With no real room to add or run another circuit, and yet I still needed a 50 amp plug for the welder, I solved both needs this way:
The solution came to me while I was at a garage sale. On the $1 table sat a new drip-proof Square D electrical box about 8" X 5" by 3" deep. As I lifted up the electrical box's door, there was a new 30amp breaker....
So, I mounted that breaker box on the back side of the jointer. I unwired the jonter's 30 amp plug and cut the 6' cord into two pieces. I ran the shorter motor wire in the bottom of the breaker box and to the breaker and the longer cord into the top of the breaker box. I bought a 50 amp plug at Home Dep. and attached it to the end of the longer wire going to the jointer.
Now I have a protected 30 amp circuit mounted on the back of the jointer, and when/if I need that 50amp wall socket for my #8 extension cord to run my welder, it's still there, too.
I LOVE GARAGE SALES....
Bill