I got a problem, one for which I’ll be hiring an electrician. However, I’m wondering if any of you can help me diagnose the problem. I’m renovating a 2-family townhouse. The project that is causing all the trouble is my central ac, specifically the wiring powering the two compressors. I have two meters, and two panels, with 100 amps in each panel. The two compressors are in the backyard. One requires a 20amp circuit breaker, the other one requires a 40 amp breaker, both 2-pole. The 20amp circuit is wired with 10g wire, the 40amp is wired with 8g wire. Both compressors have a 60amp disconnect nearby. The wire run is about 80 feet. The two breakers are in separate panels.
So here is what happened– The ac contractor arrived today to activate the smaller of the two units. With the disconnect turned off, I turned on the breaker in the panel-no problem-the disconnect reads 220 v when I put a meter on it. But when the disconnect is switched on, the breaker in the panel trips, loudly and with a big flash. If I try to then switch the breaker on, with the disconnect in the on position, snap, pop, whoa. Thinking that maybe I had a short in the wire run, I ran a length of romex along the ground to check that. Remaking the connections with the new run, same thing.
Now here comes the scary part– Thinking that I should check whether it was possibly something to do with the panel or the breaker, I remade the connections at the panel to the other panel-the 40amp breaker meant for the other compressor. This time, when I switched that breaker, with the disconnect on, the was flash, poof, maybe a bit of flame and definitely some smoke coming FROM THE METER directly below the panel, not the panel like before.
So anyway, this all seems to be above my paygrade. I’m just looking to get some opinions from some folks before I go paying for them. I am curious if this was my screw-up, or something else. Thanks in advance, and thanks also to all of you who had some advice for me at the beginning of this project.
Pat O
Replies
From the incomplete info you provided, my guesses are:
The disconnects or the feeder breakers, or both, are miswired.
This created a direct line-line short or ground fault.
You have ruined the breakers by closing them on a fault repeatedly. Have the electrician replace the breakers.
It's not likely you got two bad breakers. It's not likely that you got two bad disconnects.
How'd you wire the disconnects--type of cable, which color wire to which terminal in the disco?
You need to have more fundamental knowledge of electrical wiring. Try the Ortho or Black and Decker home wiring books for the fundamentals, then Rex Moore's "Wiring a House" from Taunton Press. (NO, they don't pay me to say that). Then check the Fine Homebuilding online archive, which you have to pay for, or go to the library and read the back issues.
BE advised that often electrical wiring can be amazingly screwed up--installed very badly--and actually work. But the redundant safety that code requirements and the right installation techniques provide may be absent. One thing goes funny and it's a shock, an electrocution, or a fire.
Cliff
At the breaker in the panel, i did not think it mattered which wire went where on a 2-pole breaker, that both where hot legs. I'm assuming this. At the disconnect I wired the black wire to the breaker in the disconnect and the white wire to a lug next it. Thanks again guys.
You wired the feeder conductors to the breaker terminal and to ground (the lug).
You created a direct short, AKA a bolted fault.
What did Dirty Harry say? "A man's got to know his limitations."
You're in over your head on a 240V circuit. How about all the other wiring? Even if it works, it may not be safe. I recommend having an electrician thoroughly check your work.
Be advised that a municipal building inspection is just a spot check, and sometimes a lot less than that. Passing the building dept inspection is far from a guarantee that the work is done right.
Cliff
It's really disturbing when people mess with stuff they shouldn't be messing with...
It is common to miswire the service disconnects on air conditioners.
Not all "line" and "load" terminals are in the same place between the different manufacturers, and people in a hurry make assumptions.
I have seen sloppy connections making contact where they shouldn't.
I have also seen wire pinched and resulting broken insulation between metal covers and boxes.
All of the above can be traced to someone in a hurry.
While possible, outright defective components from the manufacturer are not very common. You are lucky you didn't get hurt messing around and you may have caused additional damage.
On such a long wire run, I would have sized the wire for the LRA of the compressors. The wire may buzz in the conduit at start-up, and there will be voltage drop at start up, which will kill the compressor... especially at low voltage conditions when everyone else has their AC in use. I do things so it works past the standard 1 year warranty.
From what you said, if i'm reading it right, sounds like you have a short on the A/C unit side on of the disconnnect.
Many times I've seen a mis-wired disconnect switch.
P.S. sent to wrong person. sorry.
roger
Edited 6/12/2008 11:57 pm ET by roger g
Yep, I still have a little ways to go on the learning curve. The electrician who I brought in saw the problem right away. He also took a look at the rest of the house and put my wife's mind at ease. Thanks everybody.
Don't feel too bad because I used to correct the problems the electrician caused. Mind you, they couldn't turn the a/c unit until I was finished so they really didn't know they made a mistake.roger