A Wiring Lesson

BandJCarm · 07-25-2016, 10:45 AM

First, I know less about electrical stuff than I do plumbing. I know TWO things about plumbing.

But the electrician just left. And if this helps anyone, good........it won't apply to most of you, but I bet it does to some.

I had a 30 amp receptacle on outside of garage wall for the old camper. The important thing to note is that the garage was added later. Technically it connects to the house, but think of it as a detached garage. It has it's own breaker box, fed from the house main breaker on a 100amp breaker. Inside is lights, plugs, a freezer, and a 'beer fridge'.

I had the same electrician come out and replace it with a 50 amp RV plug, for the new fifth wheel. He just left.

Running new wire, putting in the receptacle, running outside metal conduit.......all that went fine. No problem. BUT.........

When the garage was built, the wiring they used to connect the 100 amp breaker(s) was/is ........(I don't remember the gauge he said, sorry) made to handle about 30-35 amps, per the electrician. He said "The wire will burn up before the breaker is tripped".

Uh Oh!

So they are estimating costs to run new heavier wire and put in a dedicated breaker at main house, with new HD wire to handle it. And I'll get that done.

In the meantime, I'm running just one A/C as we get ready to leave for Goshen......when I get back, he'll come put in the new stuff. I plugged the EMS to it, and turned on both A/C units for a minute, to see what it was pulling. It was hitting about 16a on L1 and about 14-15 on L2, with lights and both a/c. So it carried it ok, but at the upper limit of the wire. So, I turned off 2nd a/c and I'm well below 20a.

Moral of the story? Putting in a 50 amp receptacle and breaker is not sufficient. The house wiring has to be able to carry it.........

And that's why I'm not an electrician, and use one I can trust. He could have put it in, and left. But he has done work for us often and is very honest, and good at this. So he checked all that first and maybe saved me a house.....or at least a garage.

The End.....

roll credits

**Herk7769** · 07-25-2016, 10:48 AM

Odd they fused the garage at 100 amps when the service was run with 30 amp wire. Could just as easily placed the correct 30 amp 220VAC breaker in the box as the main...

BandJCarm · 07-25-2016, 11:01 AM

Yes.

But here's what I think. We've 'added onto' this house about 3 times. Today it hit me. The wire comes out of the old part of the house on an exterior wall, and is buried over to the newer garage. SHOULD have been run inside but wasn't. That always puzzled me. Today (after 30 years, told ya I'm slow) I saw why. The wiring is right beside the pad for where the outside a/c unit USED to be. So I think they did it on the cheap and tied into that.

Regardless, stupid as it is, that's how they did it, and it coulda been bad........

itat · 07-25-2016, 11:44 AM

BandJCarm, I'm a bit confused (doesn't take much). If they re-used a circuit that used to go to an old A/C, then that circuit should have been on a dedicated breaker, probably 30A, in the house. You said you have 100A breaker(s) in the breaker panel in the garage and they re-used the wiring to the old A/C, so did someone replace a 30A breaker in the house with a 100A breaker? Or is the garage protected by a 30A breaker but they used a new box in the garage that came with a 100A main breaker?

BandJCarm · 07-25-2016, 05:07 PM

Quote:

Originally Posted by itat

BandJCarm, I'm a bit confused (doesn't take much). If they re-used a circuit that used to go to an old A/C, then that circuit should have been on a dedicated breaker, probably 30A, in the house. You said you have 100A breaker(s) in the breaker panel in the garage and they re-used the wiring to the old A/C, so did someone replace a 30A breaker in the house with a 100A breaker? Or is the garage protected by a 30A breaker but they used a new box in the garage that came with a 100A main breaker?

Well, those are great questions, but I can't know for sure now.......but what I meant was they put in a 100a breaker in old house, and a 100a breaker in newer garage, and then (stupidly) thought "OK, now how do we connect these suckers?"

And then they said "Oh look, here's some wiring that already goes into the house, let's use that".

This is supposition as to why. But it is real as to what it is............

itat · 07-25-2016, 07:45 PM

I'm not an electrician but I do know this. In both breaker boxes, the main breaker is usually at the top of the box and will be the largest amperage breaker in the box (typically 100A or 200A). All the other smaller breakers in the box feed the various individual circuits (branches). The individual circuits usually have breakers ranging from 15A to 30A and may occupy 1 or 2 slots. A single slot (single pole) breaker is for 120 VAC and a double pole breaker is for 220 VAC. The old A/C would have been on one of those circuits, maybe with a 30A, 2-pole breaker.

The breaker box in the garage would be a "sub-panel" fed from the main panel in the house. I found these videos that show how to wire up a sub-panel.

https://www.youtube.com/watch?v=bDuOVe19C8M

https://www.youtube.com/watch?v=suf9F2Hev50

So, when you said "they put in a 100a breaker in old house, and a 100a breaker in newer garage" I can't figure out if the 100A breaker in the house is for an individual branch circuit or the main breaker for the entire box. I would hope you have 200A service in the house and they have a 100A 2-pole breaker feeding the sub-panel. The sub-panel in the garage should be lower amperage than the main panel in the house.

Anyway, as you probably know, if they did set it up so that you have 100A going out to the garage, it would be illegal to not have properly sized wire to handle 100A for that distance.

Hopefully a licensed electrician on here can confirm everything I've said is accurate.

Witch Doctor · 07-26-2016, 12:55 PM

You are correct

ShermanD · 07-26-2016, 01:36 PM

Question.- Are you saying that the wire feeding your garage is fed with a 100 amp breaker at the main panel or that the panel in the garage has a 100 amp main breaker?

You can purchase panels two ways, with a main circuit breaker and without a main circuit breaker. Both are perfectly legal to use as a sub panel.

According to code the wire "Feeding" the secondary panel must be fused at or below the amperage rating of the wire. Nothing in the code says that the sub panel needs to be fused at the feed wire amperage rating.

A 12 circuit panel and up will be either not have a main breaker or a 100 amp or larger main breaker.

If I understand your dilemma correctly, your wiring to the garage is sized for a 30 amp breaker and is fused at 30 amps which is perfectly legal.
If a shyster electrician decided to fuse 30 amp wire at 100 amps when the new garage was built you are really lucky you didn't have an electrical fire.

If the 30 amp wire is indeed fused at 30 amps then your electrician is just upgrading your garage service to 100 amp wire along with a 100 amp breaker at your main panel.

I am a retired electrician and I have a `1200 sq ft man cave out back, I ran a 100 amp service from my basement out to the building but I only have a 60 amp breaker at my main panel feeding the garage.

Why? Because it is perfectly legal and I ran the 100 amp service more to adjust for voltage drop, because the sub panel is 100 feet away from the main panel, and I did not want a 100 amp capacity sub panel fed off my 150 amp service, although it would be perfectly legal to do so.

The only thing that draws more than 30 amps is my buzz box welder that I rarely use more than a couple times a year so I have no need for more than a 60 amp main breaker for the garage.

You may also like: