We are having some heting and air conditioning work done. Going green with a gorund source. Some of the existing wiring is too short. The installer said he had to run new wire. My question was why not use junction boxes to extent the existing runs?
He said that junction boxes were unsafe. I have a number of junction boxes in the house. Are junction boxes safe?
I m a little unsure of his knowledge since he wired a 34 Amp circuit using 10GA wire and a 30 Amp breaker. He was upset when the breaker blew in 5 minutes of power on. He said he would have to come back and install a 40 Amp breaker in the box but thought the 10 GA wire was still OK.
Thanks
Replies
It's generally best to avoid unnecessary connections/junctions in high-amperage wiring. I've never heard quoted chapter and verse as to when junctions are/are not allowed, though.
Re the 34 amp circuit -- there are a few variables there, and it may or may not be OK, depending on what the load is, etc. Would certainly be more comfortable with #8, though.
Well, 10 ga is almost adequate: rated at 33 amps "enclosed" (http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity) and 55 amps free air (think overhead power lines).
Junction Boxes: Maybe. Is this indoor or outdoor wiring? Sealing a weatherproof junction box could be problemmatic. Buried cable? They DO make waterproof rated shrink tubing to seal connections.
What is the voltage? That too could make a difference.
And don't forget: depending on where you live, an "installer" might not be permitted to do that sort of work.
Maybe think ... permit. Did he get one? The BO would rule on the jbox and the wire size and the circuit breaker rating.
You're right to be cautious, IMO. You're taking the first steps to ensure you're not getting short changed.
Generally, I think it would be incorrect to make a blanket statement the J boxes are "unsafe". That is absurd, I think. Houses are filled with them. No different splicing a wire than wiring a series of lights or whatever. Maybe he has an opinion and comfort level with the particulars you're working with, but he's not expressing that. Maybe he should have said something like ... I'm not comfortable w/ a J box for this particular application and briefly explained himself so that you would be comfortable.
If the wire is 10ga
then the breaker needs to be 30A.
It sounds like you have someone who knows enough about wiring to be really dangerous!
All I can say is get a LICENSED Electrician NOW before this guy hurts himself,
or you and your family!
Electrical safety is no joke, it's what the national electrical code is all about.
You need someone that knows how to do code worthy work.
ONLY an Electrician who keeps up with the code change cycles is going to be able to do that.
Believe me there are NO unlicensed individuals who can do a code compliant electrical installation.
They Just don't have the proper knowledge and training to do it.
Some Installers Do Know Code
Depending on the state, a Licensed HVAC installer will know the electrical code, particularly as it relates to their specialty. The licensing boards do test them on it, and require continuing education courses, just like they do for the licensed electricians.
Holmes gets a major woodie everytime he sees one. As you pointed out a J box is really no different than an outlet wired in series. I think the major issue is they not be buried in the wall such that if there is a problem that it can be detected. So if you are cheap and don't want to re-wire then you need to be okay with having a bunch of blank wall plates in random spots.
There is something unusual about HP motor loads....My installation instructions called for #10 (although I used #8), protected with a 50A breaker. My inspector didn't seem concerned... but didn't explain anything (he hated homeowner permits).
Of course this went against everything I understood, but I went ahead with the installation.
Then I found a table at the back of the code book which explained wire sizes and breaker ratings for motor loads... sure enough..there was #10 and 50A.
Perhaps one of the EE guys around here can explain the theory behind this.
There's overload protection and short circuit protection.
A wire can briefly handle a current load that is several times it's normal rated load. In a short circuit situation, eg, a #10 wire might briefly see 100A or more. The breaker needs to be "small" enough and sensitive enough to trip before the wire overheats and melts.
A steady-state overload is more stressful -- a #10 wire in standard NM cable has an ampacity of about 33 amps (probably closer to 38 in average use, after the fudge factors are removed). A current only a 2-3 amps over that ampacity will eventually (over minutes, hours, or days) cause the wire to fail in some fashion (melted insulation or failed connection are most likely).
An air conditioner compressor may need near 40A for 15 seconds or so (longer than the trip time of most breakers) when starting, even though it runs at 25A. Inside the compressor is a sort of thermal circuit breaker that will trip if the unit runs more than 30A for more than about two minutes (just to pull numbers out of the air). This thermal circuit breaker protects the #10 wire from steady-state overload (assuming no other loads are on the circuit), and so the breaker in the panel only needs to protect against short-circuit situations (and a 40A breaker is sufficient for this).
Whether this is a good idea or not is subject to some question (though it's done all the time). The smaller wire reduces the voltage available to the compressor at the moment of most stress (starting), making life harder for the compressor and very likely reducing it's lifetime by maybe a year or so. When the compressor is close to the panel (ours is only 15 feet away, eg), the smaller wire is probably fine. But if the unit's 80 feet from the panel then you're looking at a 5% voltage drop, and you can cut that voltage drop about in half by stepping up one wire size (down one number).
Thanks a mil for that..... and I'm still glad I opted for #8.