I’ve got a spare 30amp circuit for kitchen appliances that I would like to use for my porch radient heaters. I have two 1550 watt (two 700 watt elements, and a 150 watt halogen light) heaters that plug into 110v outlets.
The 30 amp line has a red, black, and white stranded wire (10 ga, I think). The breaker has two levers bound together.
I would like to run the red/white to one heater, and the black/white to the other – with ground wire to each of course. Would this work correctly – as in if one of the heaters shorted out, would the breaker trip correctly?
Rebuilding my home in Cypress, CA
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Replies
Well there are a couple of issues.
You would need to replace the breaker to one of 20 amps.
But the real problem is that you don't have a ground unless this is run in metalic conduit.
"run the red/white to one heater, and the black/white to the other - with ground wire to each of course."
Yes, each one will be grounded. This is circuit dates from early 1960, so I guess they counted on the shield being the ground. I would be running an actual ground wire on each connection.
The problem that I have is that these heaters use too much power for a single 20 amp circuit, so I'm curious why I would swap out a 30 amp breaker for one that would not handle the load? The point of this is that 30 amp available circuit will safely run this 3100 watt heating array.
Basicly I am looking to split the 30 amp breaker into two 15amp lines - both getting interupted if either side has a problem. I'd like to not have to open up the breaker box, take out this big circuit, install two new breakers, and install two new circuits. Do you see what I'm saying? I'd like to use this circuit as is, just splitting it at the end between two heaters.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Edited 5/10/2005 10:38 pm ET by xxPaulCPxx
You said you have two 700 watt heaters and a 150 watt lamp to power, all 120V. 700 watts is a little under 7 amps at 120V. So put one heater on one leg and the other heater plus the lamp on the other. You have 7 amps on one side and 8 on the other. Definitely no need for a 30 amp service, and using a 30 amp breaker to supply those loads is not legal since they should be breakered at no more than 20.[Oops, missed the point that each of the **two** heaters has **two** 700 watt elements, but that just runs the total current on each leg up to 14A or so. Well within the margin for a 20A breaker (though a 15A would be a hair tight.]I think your point of confusion is with regard to splitting the circuit. Splitting a 30A 240V circuit gives you two 30A 120V circuits, you don't split the current.Opening up the box and swapping out the breakers is no big deal. You can replace the 30 with a ganged 20 or with two separate 20s.[But, with dual-element heaters, it would make more sense to wire them as 240V units, if at all possible. This would reduce voltage drop and simplify your wiring somewhat. The lamp can be run off another circuit.]But, having said that, it sounds like your comprehension of all this stuff is not very great, so you had better get someone knowledgeable to help you.
Edited 5/10/2005 11:01 pm ET by DanH
I went back and rechecked my wiring book, and checked up on "Safe Capacity". I realize now that both heaters, running full out consuming 3100 watts, would require 26 amps which is just a hair over (2 amps) the Safe Capacity of a 30 amp breaker.
But this raises another question. Since there is nothing else on this circuit - no motors to surge or other outlets to pull more amps - would it be OK to exceed the Safe Capacity slightly on a dedicated circuit? BTW, just to help understand this application, these heaters would run 4 hours a day TOPS. It keeps an outdoor dining area warm.
The existing breaker has two switch levers that are joined by a metal bar, and it occupies two slots on the bus. Intresting that both lines are 30 amp, instead of 15 amp on each wire.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
"But this raises another question. Since there is nothing else on this circuit - no motors to surge or other outlets to pull more amps - would it be OK to exceed the Safe Capacity slightly on a dedicated circuit? BTW, just to help understand this application, these heaters would run 4 hours a day TOPS. It keeps an outdoor dining area warm."The 80% safety factor is require on "full time" loads. Full time is anything 3 hours or more of operations."I went back and rechecked my wiring book, and checked up on "Safe Capacity". I realize now that both heaters, running full out consuming 3100 watts, would require 26 amps which is just a hair over (2 amps) the Safe Capacity of a 30 amp breaker.The existing breaker has two switch levers that are joined by a metal bar, and it occupies two slots on the bus. Intresting that both lines are 30 amp, instead of 15 amp on each wire."But you still are not understanding this.#10 wire is has a nominal rating of 30 amps max. It does not matter if it is 120 v, 240v, 480, or even 12 volts. It is still rated at 30 amps.You circuit as it is now can supply a maxinum of 30 amps on either hot with the return via the neutral or on both at the same time. In that case the current in the neutral will be zero, because the two nots are on different legs they cancel each other. Or you can have a mix, 30 amps on one leg and 20 on the other and 10 amps in the neutral. But each leg is limited to a max of 30 amp.So 30 amps at 240 = 7200 watts maximum on that circuit (ignoring the 80% rule).Or two 120 circuits of 30 amps each.30x120 = 3600
30x120 = 3600
Again for a total of 7200 watts.However, those heaters are wired for use on standard 15/20 amp circuits. That is why I am saying you need to replace the breakers with 20 amp breakers.And with that you would have TWO 120v circuits, each with20 x 120 x .80 = 1920 watts.EACH circuit could easily handle the heater and a 150 light.
Thanks for the Breaker 101! the 30 amps at 240 volts was a key that I missed.
But I'm still confused on this point:
If the circuit can handle a total of 7200 watts (or 5760 safe),
If I will be using less that 30 amps at 120v on each leg
Why would I replace the breaker itself? If my application will only draw less that the system can safely provide, why would I need to replace a higher capacity part with a lower capacity one? If I am using a 20 amp appliance on a 30 amp capable circuit, isn't that similar to using a 10 amp appliance on a 20 amp circuit? Why would I need to reduce the total capacity of the system?Rebuilding my home in Cypress, CA
Also a CRX fanatic!
The wiring inside the heaters is only certified (by UL or someone similar) to be safe on a 20 amp or smaller breaker. If a fault occurs in the heater, the design is relying on the presence of a 20 or less breaker to help prevent a fire.
Because with a duplex receptacle you can plug in 30 amps of load, but they are only desgined to handle 20 amps.Even 15 amp duplex receptacles are designed for 20 amp feed through and can be used on 20 circuits.That is the ony except. A single 15 amp receptacle can only be installed on 15 amp circuits.Multiple 15 amp receptacles can installed on 15 or 20 amp circuits.20 amp receptacles can only be installed on 20 amp circuits.30 amp and 50 amp receptacles can only be installed on 30 amd 50 amp circuits, respectfuly.BTW, you now have, what is called a multi-wire circuit. You can not feed the neutral through the receptacle. You have to pigtail it to connect to the receptacle (and continue on - in your case the other receptacle).If you do not have both hots on any one receptacle you don't need to use a 240 breaker, but can use 2 separate 20 amp ones. But there is a certain amount of safety for anyone that works on it in the future to know that the whole box is dead by using 240 breaker.If you don't use a 240 breaker I would mark next to the 2 on the panel that it is a multi-wire circuit.
I see what you are saying about the 20A duplex receptical (a real 20 amp, not a 15 amp). However, since the 20A receptical can be "broken out" by removing the tabs, won't you have two seperate 20A individual outlets each capapble of independently providing 20A of throughput?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Yes, you could run two separate 20 amp circuit to a 20 amp receptacle by breaking the tabs on both hot and neutral.And you could pull a TOTAL of 40 amps.But on part in the receptacle would carry more than 20 amps. So you aren't overload the receptacle.But if you have a duplex receptacle on a 30 amp circuit them you can pull upto 30 amps through the connections.
Thanks for being so good at answering these questions - I hope they're not too dumb. This is still a mental exercise - I don't have the strippers in my hand... yet ;)
OK, so IF I connected the existing 240 breaker to my heaters by running each hot to a different heater and splitting the neutral between the two, I would be running 120v, 30 available amps to each unit, with a negated current on the neutral if they were both running at the same wattage. As I now understand it the weak link would be the internals of the heaters themselves. a moth could fly in and cause a little bitty short, just enough to make it run at say 21A - fine for the circuit but deadly to the heater. Without actually shorting out, the unit could heat past its design limits and potentially cause some damage. Poof goes the house!
Now, If I didn't want to dink around in my breaker box or buy two new 20 amp breakers, couldn't I protect the appliances at the end of the line instead of the head? Instead of modifying the breaker box, couldn't I just install a 20A Microwave oven fuse in 20A fuse (about $11 at Radio Shack) holder between the 10ga wire and the receptical? This would keep everything intact, yet limit the receptical from serving anything above 20A. It also keeps all the work, wiring, and potential probelms (this house is full of them) on one end of the circuit instead of both ends. Kookey mabey, but is this a workable solution?Rebuilding my home in Cypress, CA
Also a CRX fanatic!
"As I now understand it the weak link would be the internals of the heaters themselves. a moth could fly in and cause a little bitty short, just enough to make it run at say 21A - fine for the circuit but deadly to the heater. Without actually shorting out, the unit could heat past its design limits and potentially cause some damage. Poof goes the house!"I have never seen the UL specs for a heater so I don't know, but I suspect that is not the problem.First a 20 amp breaker won't trip at 21 amp. They can go for several hours at 10-20 percent overload.I suspect that the problem is under fault conditions. It might be a "dead short", it might be a break in the heater wires that allow it to short out about 1/2 of the element and thus draw much more current.Now electronic components under surge or fault conditions are rated by by I**2t. That is the amount of energy that they can absorb before melting. By going having them connected to a 30 amp supply rather than a 20 amp supply they can be have 2.25 times the energy delivered to them before the breakers trip.What you are proposing should probably provide the same saftey, as far a fault in the heat, but would not be anywhere following code.In addition you add 4 more connections in series and you have to find a place and manor to mount the fuse holders without crowding the box. Also you have added an overload device that is not in a a common place and any failure will drive the user crazy trying to find it.I think that you have doubled your troubles.If you wanted to go to the effort you could install a small sub-panel.
And two 20 amp breakers should cost about the same as the microwave protection thing, along with being much easier to install.
Basically, the problem is this: If you're not competent to open up the panel and replace the breakers, you're not competent to do any of the other stuf you're talking about.
Never said I couldn't do it... I'd just rather not.
I'd like to hold off any projects involving the breaker box until AFTER I replace that old rusty thing. Did I mention that the cover fell off? Nice.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
I'm certainly not an expert, but in essence wouldn't the lower amp breaker (20) essentially be protecting the heater first and the wiring itself secondarily? So if the heater malfuntioned and draw exceeded 20a but not 30a, it would pop.
Interesting discussion.
PJ
Everything will be okay in the end. If it's not okay, it's not the end.
Breakers are designed to protect the wiring not the loads.However, the heater is designed and tested for use on circuits that can't supply more than 20 amps.
Sorry I missed the ground. You said "shield" is that run in BX?The reason that I questioned that until 1996 range and dryer circuit where typically not run with a ground, 2 hots and a neutral. Some locals and some types of installations did require a 4 wire (ground) circuit, but most commonly they where only 3 wires." heaters that plug into 110v outlets"Most equipment that plugs in has 15 amp plugs which can either go into 15 or 20 amp receptacles.And you can not use those on 30 amp circuits. That is why I suggested changing the breakers to 20 amp.I see that Dan has explained what the watts/amp relation is for this type of application.
Yes, it is BX sheilded 3 wire.
BTW - Thanks for all the great information so far everyone! I've done alot of wiring, but none that dealt with a 240 circuit, so thanks for the handholding.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Edited 5/11/2005 3:44 am ET by xxPaulCPxx
>>But the real problem is that you don't have a ground unless this is run in metalic conduit.I had though metallic conduit wasn't technically considered a ground.Am I missing something?
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First of all there are 3 types of metalic conduit. EMT, Intermediate, and ridgit. But in home applications is is almost always EMT except for the riser/service entrance which is one of the heavier versions.EMT is jointed with "clamping" connectors (there several style of fittings, but all use pressure in way one or another). The other two can be threaded or a threadless connector used. I have never worked with other than EMT so I don't know anything about the threadless connectors.However, in all 3 types the conduit (and connectors) are listed as being equipment grounding conductors. However, some people (and it might be in some local codes) feel that connections on EMT can be come loose and will run an ground wire in addtion.Just to round this out both AC (commonly called BX) and MC are listed as grounding conductors (AC the armor, MC "the metallic sheath or combined metallic sheath and grounding conductor")But I understand that some local codes (IIRC Georgia is one) limits AC to 6ft when using as a ground. There might be more restrictions in new versions (I have 99 code).Liquidtight and flexible metallic tubing is listed for grounding, but limited to 6ft. The connectors have to be listed for grounding and there are several other reqirments.
I get the impression that most areas now require a seperate ground conductor, even with any type of metal conduit.However, the other part to keep in mind is that any metal component in the system must itself be bonded to ground, even though it cannot be the ground for the curcuit.
Bill, great info.Thx.
Paradigm Inspections, llc View Image
Sojourners: Christians for Justice and Peace
Is there a 4th ground wire?
I come up with 13 amps for each heater unit You might want a 20 amp breaker. That is replace the 30 amp breaker with two 20 amp breakers. The 30 amp wires [#10 guage] can handle 20 amps. The neutral sholuld carry ~0 with both units on, but the breakers must be on different phases. I like your idea. I think it's a great idea. You will even have less voltage drop.
~Peter
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