Hello all,
I am an avid do it yourselfer and at times get ahead of my ability.
I recently upgraded my furnace / a/c unit to a heat pump. I had a contractor do what I thought to be the bigger part of the job, and decided to go it myself on the electrical upgrade. my old furnace/airhandler was 120 service and I was told that the new airhandler was 240. not a big deal…. I was able to put the 60 amp circuit in the existing box (had that upgraded professionally last year) I did this with a joined 30 amp circuit (if I am using all the wrong terminology my apologies) (two 30 amps with a tie) to give 60 amp service to the air handler. I used 10 guage wire over a 50ft span to connect the breaker box to the shut off switch. they wired from the shut off to the appliance itself. Now, when the unit heats with just the heat pump all is good. when the appliance runs with the heat pump and the auxiliary electric heater, the circuit trips…. should I have used a 6 gauge wire instead of the 10?
Replies
Need more details-
I just purchased a 36K geithermal heat pump with aux. heat. THe heat pump is supposed to have a 45 amp breaker for the pump with the aux. heater wired separately with a 70 amp breaker. (You need to determine the electrical loads. but I think that you need a second feed for the aux. heat.
If your aux heater pulls 70 amps I hope the Porsche is paid for.
A double pole 30 amp breaker does not give you 60 amps. It will trip if either leg exceeds 30 amps. In a 240 volt system both legs are hot and carry the same full current of the load. You are running the full current through both legs, not half current through each one.
I don't have the tables with me and cannot answer your wire size question.
I use no. 8 for a 40 amp circuit. So I would think 10 for a 60 amp circuit is a little light.
As for as the breakers, i'm not exactly sure what you mean about the tie. Why not just use a 60 amp 240 breaker?
maybe this is why people hire electricians.
ok. so, if the wiring calls for a 240 volt 60 amp breaker. I need a single pole 60 amp breaker.... not a twin pole breaker with 30 amps on each side... right?
I am guessing that my heater probobly does not pul more than 45 amps, which would explain why my set up trips the breaker.
next question. If I put in a 60 amp breaker, it would have to be split so I can go 240 with it? I would also need a heavier wire?
I will have to look at the specs again to see what the unit needs....
thanks
If the wiring calls for a 60 amp 240 volt service then you need a 60 amp two pole breaker. 10 gauge wire is way too small for 60 amp service. 6 gauge is acceptable for reasonably short runs.
I think you are in over your head on this one and need to call in an electrician to make sure that it is done per code.
I think you are right.
Pride is one thing. saftey of my family is another issue altogether.
Thanks
You would need a 60amp 240 volt breaker, which would be a double pole. What may be confusing you is that both of the tied together switches would read 60, you dont add them up.
Good luck and if you're not sure consult an electrician. Its easier to diagnose on site than on a message board.
Re: "I was able to put the 60 amp circuit in the existing box (had that upgraded professionally last year) I did this with a joined 30 amp circuit (if I am using all the wrong terminology my apologies) (two 30 amps with a tie) to give 60 amp service to the air handler."
Ummm. Where to start?
If this is anything like a fair description of what you actually did you need to put down the screwdriver, turn off the circuit breakers, and pick up the phone. Calling in an electrician is your best option. "joining" two 30A circuits doesn't effectively, safely or by Code get you 60A.
Assuming you get this looked at and confirmed as correct the next step would be to snap an ammeter onto circuit and compare it to the manufacturers specification label for the unit and any heat strips.
alright. the electrician is on the way.
Now. just so that I know (I can;t stand not knowing)
double pole 60amp breaker for the 240 service to the unit. The aux heater when running draws 45 amps, but the book calls for an overload circuit of 60, so we put in the 60. The book also has a wire guage table. The table reads that for 60 amps over 50 ft, I need a 6 awg. (this was mentioned in the thread, not sure who, but you were right). seems easy enough (but the electrician is still on the way) ..... now, I saw a calculator on-line that said it is for the purpose of determing wire guage. the variables that it asks for is the amps, and length of circuit/2. If I put in 25 (half of the 50ft length) it gives 10 awg. The table said 6, so I am more comfortable with that. Am I confused on the meaning of circuit length?
Circuit length is the total path that the electricity follows.That is the hot wire from the source (panel) to the load and the return (other hot leg of 240 or neutral for 120) from the load back to the source.It is twice the phyisical distance between them (assuming a straight run). Apparently the calculator that you used only figures voltage drop. There are also maximum ampacity (current) limits based on the size of the wire, the type of wire, and the application. That is why #10 is not acceptable.
The code states that #10 gauge conductors must not be fused at more than 30 amps (section 240.4d). In residental applications, #6 gauge wire is generally good for a 60 amp run provided the length does not exceed a 5% voltage drop reduction. The voltage drop is primarily caused by the resistance in the wire itself. If the drop is too high, a larger conductor must be used. There are also other factors that need to be taken into consideration when choosing the proper wire such as the # of conductors in a raceway (conduit), ambiant temperature, etc.
So, if you are not sure, it's better to be safe than sorry and have a qualified electrician do the work. You did the right thing.
okay..... now for the Dumb question of the year (Can I possibly profess more ignorance???)
What is the effect of using a wire that is too small for the job?
ie. 60amp through a 10awg? or to reduce any question of "it might work in the right conditions" 100amp through a 14awg......
does the wire melt? will it arc through the insulation? will it just continue to heat untill it burns down the house?
Think of how a toaster works: current flows thru a small high resistance wire causing it to heat up and glow. Now consider the 100A flowing thru a small 14ga wire for a long period of time. Maybe not as dramatic, but you get the picture.
if the wire goes underground, you'll always have a strip of melted snow in the winter, lights will dim when the unit kicks in, and the unit will fail prematurely. or it will burn down the house.
"does the wire melt? will it arc through the insulation? will it just continue to heat untill it burns down the house?"Will high enough current it the copper will melt.But that is 166 amps for #14 and 333 for #10.The basic factor that affects the current rating of the wire is the tempature limit of t he insulation.At rated currents there is some heating of the wire and thus the insulation. Now there are different types of insulation which have different temp limits. And there are installion conditions such as if the wire is in conduit or a cable or bundled with a bunch of other wires where it can't disapate the heat as well as a single cable which affects the insulation temp and thus the current rating for that installation.