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Wire too big for breaker

Posted by frankrey1 (My Page) on
Sat, Jun 6, 09 at 10:24

I have run about 250' of #6 THHN in conduit to a sub panel from my main panel. This will be to run a pool pump. I bought 30 amp breakers. The trouble is the wire will not fit in either breaker. One is Cutler-Hammer the other Square D. What can I do? Also I used 8/2 UF to wire the receptacle at the pool. Will I have any problems wiring the receptacle with this wire size?


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RE: Wire too big for breaker

A couple of points right out of the chute:

1. Why do you have two breakers? If your run is to feed a subpanel, you should have one two-pole breaker, not two separate breakers. It is potentially dangerous to use two independent breakers that are not designed to trip simultaneously because one pole will remain hot even after the other trips. (I may have misunderstood what you meant by two breakers, but just wanted to make sure!)

2. Secondly, why 30-amp breaker(s)? Is it because the subpanel is rated for only 30 amps? If so, your best option may be to pigtail a short length of #8 or #10 in the main panel enclosure. It's not a great solution, but it's better than shaving the skinned tails of the conductors.

Unless that panel can't handle more than 30 amps, it'd be better simply to increase size of the breaker. The purpose of the breaker at your main panel is to protect the #6AWG wire. If it's copper, a 50-amp or 60-amp double pole breaker is what you want for that purpose. (For aluminum, then 40-amp or 50-amp.) If you want to reduce the amount of available power elsewhere, leave that "job" up to the breakers protecting the branch circuits at the subpanel.

If minimizing voltage drop was your objective in selecting #6 for a 30-amp feeder, using a larger breaker doesn't affect that. If you're only actually drawing 30-amps, then so what?

Finally, I doubt seriously that the 8/2UF run near the pool meets code. Without knowing more of the specifics, you almost certainly need conduit there instead of direct-burial cable.

What kind of receptacle is it? If it is an ordinary 15- or 20-amp duplex receptacle, then yes, you'll probably find it hard to wire satisfactorily with #8.


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RE: Wire too big for breaker

You need to go to at least 35A to get #6 into a Square D QO breaker.
As Tom says, that's really what you want to do.

Again why two breakers? First you have to use the right breaker for the panel (they are not interchangable). Second, the subpanel doesn't typically need its own breaker on the feeder, but you can do that. However, if you are going to backfeed a breaker in the subpanel you need an additional mechanical fastener to keep it from being removed hot.

And Tom is right, 8/2 UF is most certainly illegal for most near-the-pool uses.


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RE: Wire too big for breaker

Thanks for the info. I will increase the size of the breaker at the main where I am connecting with #6 wire. I jumped the gun on the sub panel breaker. I will be using smaller wire on that anyway. The sub panel is rated 100 amp and the breakers were both two pole. The run from the sub panel to the pool is pretty short. Which is a good thing since it looks like I will be doing some more digging. That UF was expensive to.


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RE: Wire too big for breaker

Hopefully you ran four runs of THWN out to the subpanel.
Where is this subpanel mounted?
What is this subpanel feeding?


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RE: Wire too big for breaker

Yes I ran the required wire. I mounted the subpanel on a wooden post about 15 ft from the pool. The sub panel is feeding the pool pump on one GFCI circuit. I do have another circuit running out to my camper. I went back to my local Menard's to pick up a larger breaker. The terminal was much larger on the new breaker. Just for grins I thought I would check out the 30 amp breaker bin where I had grabbed the original. Turns out there were two different size terminals on the same size breakers. Go figure.


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RE: Wire too big for breaker

That must have been the CH breaker. I guarantee that the QO130 will not accept #8 wire.

Hopefully you've put in an appropriate ground for that post. This is considered a separate structure in most places and having a subpanel with multiple circuits is going to require it. UF is not allowed for any of the pool requirements and you can't direct bury anywhere near the pool even for unrelated circuits.

I'd GFCI the camper circuit as well. Campers are also notoriously loosy goosy with their electrical use. If the receptacle you are installing is 120V 15 or 20A it's required anyhow.


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RE: Wire too big for breaker

It was a CH breaker. I did put a ground rod in for the sub panel. How far away do I have to be from the pool with unrelated circuits?


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RE: Wire too big for breaker

CH does make a 2-pole residential breaker that is really a pair of single pole breakers permanently fastened together. The trip mechanism and handles are mechanically interlocked. If either breaker trips, the trip mechanism of the second breaker is also triggered. The handles are interlocked so that both breakers must be operated at the same time.

The main application for this breaker is for 220/240 Volt circuits where both hot lines are interrupted and the neutral/ground is not. Common useages are electric stoves, water heater, central air conditioner, air compressors and shop equipment.


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