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Forum topic by woodbutcherbynight posted 09-11-2016 03:30 PM 2921 views 0 times favorited 32 replies Add to Favorites Watch
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woodbutcherbynight

2465 posts in 1876 days


09-11-2016 03:30 PM

Topic tags/keywords: resource tip

Yesterday my neighbor calls me in a panic to tell me how his breaker box caught on fire and wanted me to come up and see about getting a new one installed. As you can see from the picture the box got HOT, Chernobyl hot people! Those that work with electricity can tell immediately what was wrong, for those that do not allow me to explain what went wrong and how it applies to expansion of our own shop electrical.

They had replaced the HVAC service breaker at the compressor with a 30 amp breaker because the old one did not work. Inside the main breaker box this breaker was fed power from another 30 amp breaker. The unit was marked for a maximum of 20 amp breaker. In such cases more is NOT better. The problem was with the compressor, it has died and when engaged draws high amps trying to work. By using a 30 amp breaker verses 20 amp the wires of the circuit now carry more amps than needed creating HEAT. Bypassing the breaker and forcing the unit to work created a lot of heat from the high amp draw of a bad compressor. Left unchecked the box continued to heat up until melting point, then the fire starts. Fortunately the homeowner was able to respond quickly and put fire out, then kill the power. Four hours of work and we had rewired the new panel and had power minus a/c.

Lesson to be learned. Sure just upping the breaker to higher amps gives you what you need for power but the wiring to that breaker has limits. If and when a tool or device shorts the breaker with correct wire will support the brief overload and shut down. But when you ignore this and have smaller wire and higher amp breaker you create heat, and electrical fire can and often does result. The device need not be drawing excessive amps to create a problem. The combination of excessive draw on smaller wire with higher than rated breaker is a disaster in the making.

While I am not a pro in this regard I do know the basics and by ignoring them we invite disaster. Sure it costs money to have a pro come and do it correctly but the risk here is at minimum your shop and house, or worse you. Having the circuit wired according to code, with the correct breaker for the appropriate load is for a reason, not merely a suggestion. My neighbor got lucky this time and has learned a valuable lesson that cost him $300 and about six hours of time repairing and cleaning up. Not to mention his wife’s reaction and subsequent rant on being an idiot. (I left as this got too heated for me.)

For those more knowledgeable on this please add more warnings or better explanations. I know it is sometimes about cost but let’s be safe, cutting corners is not a good practice.

-- Live to tell the stories, they sound better that way.


32 replies so far

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hoss12992

3832 posts in 1360 days


#1 posted 09-11-2016 04:19 PM

Very Well explained. I gotta admit I was laughing at the part where the neighbors wife started fussing at him. One thing I learned in my youth and have preached to my kids is safety first and cheap ain’t always cheap.

-- The Old Rednek Workshop https://www.facebook.com/theoldrednekworkshoptn

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woodbutcherbynight

2465 posts in 1876 days


#2 posted 09-11-2016 04:25 PM

Yeah she was not too happy about the burnt smell and it was rather strong. Finished about 2330 last night after a full day at work I was beat. Did not get any finish work done on my own projects which are many!!!!! LOL

-- Live to tell the stories, they sound better that way.

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Holbs

1379 posts in 1497 days


#3 posted 09-11-2016 04:41 PM

When I wired my garage, it took 3 months of research about electrical installs. Lots of OSHA pics of wrong doings, inspector’s summary of what they did wrong, lots of how things are to be done right, do’s and dont’s. I did everything by code to play it safe, even if it’s overkill. Because I can only assume most of the entries into electrical code are done for a reason towards safety and experience of bad doing’s

-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"

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Bill White

4459 posts in 3428 days


#4 posted 09-11-2016 05:28 PM

Wise words for sure.
There are those thing that I know, and there are things that I don’t know.
Wisdom come from being able to differentiate.
Great post.
Bill

-- bill@magraphics.us

View Mike_D_S's profile

Mike_D_S

185 posts in 1682 days


#5 posted 09-12-2016 02:37 AM

Always good to be reminded that things can happen. Just to make sure I’m clear, the root cause is that they put 30 amp breakers on both sides of a wiring run with wire gauge only appropriate for 20 amp service?

-- No honey, that's not new, I've had that forever......

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woodbutcherbynight

2465 posts in 1876 days


#6 posted 09-12-2016 02:54 AM



Always good to be reminded that things can happen. Just to make sure I m clear, the root cause is that they put 30 amp breakers on both sides of a wiring run with wire gauge only appropriate for 20 amp service?

- MikeDS

That is correct, this was an accident waiting to happen. So when the compressor died the high amps went straight to the breaker box and overheated the main bus, then FIRE. Had the correct breaker been in place it would have shut down before the wiring overheated. They replaced the a/c this afternoon and upon inspection the compressor had gotten so hot it had no paint and the metal decal plate was no longer readable.

Another neighbor commented the house was just old and these things happen. Perhaps but then he cannot see out of his right eye and has bad burns on his face and arms. Seems he tried to jump his car off one morning with a extension cord run to an house outlet. 120 AC cannot be used to “jump” a 12 DC battery….EVER!!!

-- Live to tell the stories, they sound better that way.

View Mike_D_S's profile

Mike_D_S

185 posts in 1682 days


#7 posted 09-12-2016 03:10 AM


Another neighbor commented the house was just old and these things happen. Perhaps but then he cannot see out of his right eye and has bad burns on his face and arms. Seems he tried to jump his car off one morning with a extension cord run to an house outlet. 120 AC cannot be used to “jump” a 12 DC battery….EVER!!!
- woodbutcherbynight

The electron thingy makes the spinny thingy go roundy round?

While you never want to see anyone get hurt, it does make me wish there was video…..

-- No honey, that's not new, I've had that forever......

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woodbutcherbynight

2465 posts in 1876 days


#8 posted 09-12-2016 03:46 AM


While you never want to see anyone get hurt, it does make me wish there was video…..

- MikeDS

Indeed but then I would have to go to hospital for the pain caused from laughing that hard. I hear about this stuff sometimes and just shake my head.

-- Live to tell the stories, they sound better that way.

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JeffP

573 posts in 859 days


#9 posted 09-12-2016 11:39 AM

So the compressor failure somehow produced a situation where the compressor was using more than 20 amps but less than the 30 that would have kicked the wrongly sized 30 amp breakers?

That’s kinda weird.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View becikeja's profile

becikeja

648 posts in 2281 days


#10 posted 09-12-2016 11:57 AM


The electron thingy makes the spinny thingy go roundy round?

While you never want to see anyone get hurt, it does make me wish there was video…..

- MikeDS

This video is a 480V panel, so not exactly the same, but what happened is very similar.
The wire burns and goes to ground casing an arc flash event.

Watch the video. Then respect the power.

https://www.youtube.com/watch?v=6hpE5LYj-CY

-- Don't outsmart your common sense

View TheFridge's profile

TheFridge

5765 posts in 954 days


#11 posted 09-12-2016 02:56 PM

Looks like branch circuit wiring shorted the mains out. Awesome.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View JBrow's profile

JBrow

820 posts in 388 days


#12 posted 09-12-2016 03:24 PM

woodbutcherbynight,

I trust your neighbor replaced the cable from the load center to the a/c before powering up the new unit. I would be surprised if the cable servicing that circuit emerged unscathed from the overload.

Some time ago there must have been a sale on those 30 amp breakers. When I purchased our current home I noticed about half a dozen 30 breakers protecting 120 v circuits, most of which were household lighting circuits. On closer inspection I noted that 14 gauge wires fed those circuits. Fearing an accident like that you described, I immediately replaced the 30 amp breakers with 15 amp breakers. It made me wonder what the prior homeowners were thinking; I can only guess they were oblivious to the danger.

View woodbutcherbynight's profile

woodbutcherbynight

2465 posts in 1876 days


#13 posted 09-13-2016 01:17 AM

JBrow

Yes the wiring from main breaker box to service box and from service box to new A?C unit was replaced including a new service panel. A electrician friend of ours came out and checked the work and gave a few tips on some things to get right before ever trying to sell the house. So with the exception of the a/c power circuit and breaker box my neighbor got off cheap. He does now have a healthy respect for screwing with electricity.

The old breaker box happens to be the right size for a drawer I want to make for under a cabinet. With some paint work it will look good as new. LOL.

-- Live to tell the stories, they sound better that way.

View tealetm's profile

tealetm

61 posts in 325 days


#14 posted 09-13-2016 03:08 AM

So why did the wire become hot just at the breaker location? Wouldn’t/couldn’t it have failed or burned at any point between the breaker and the load?

View nightguy's profile

nightguy

213 posts in 130 days


#15 posted 09-13-2016 03:19 AM


So why did the wire become hot just at the breaker location? Wouldn t/couldn t it have failed or burned at any point between the breaker and the load?

- tealetm

I have limited knowledge of electricity, I only made the stuff for 20 years, yes it could have, I am guessing in the breaker box was a situation of more resistance, and that is why the heat build up there, and not in the wire run.

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