Need some service entrance panel help

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  #1  
Old 12-08-06, 05:35 AM
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Location: Indiana
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Need some service entrance panel help

I have a need to replace the bus bars in my electrical panel. The bus in the one I have is aluminum, and the tabs that supply the power to the breakers are corroded and getting eaten away. My plan was that if I can find the same box, I can swap out the bus without having to go to the hassle of changing the entire box and having to repull all the wires into it.

The box I have is a Siemens G3030MB1200, which I understand to be 30 slots, 30 circuits. I can only seem to find the G3040MB1200CU with the copper bus bars (which I want). I'm not sure what is meant by 30 cicuits as opposed to 40 circuits.

My question is this - will the bus bars from the 3040 fit into the 3030 box? It sure would be nice.

Thanks!
 
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  #2  
Old 12-08-06, 07:32 AM
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First the un-asked for opinion:

Unless you can arrange for a professional (eg. an electrician or the power company) to cut the power to this panel, what you are describing is _not_ a reasonable DIY project. The service entrance conductors coming in to your main panel are _not_ protected by fuses, and are subject to very high 'short circuit' current. In addition to the shock danger that you would normally associate with a 120/240V circuit, in the event of a short circuit on one of these wires, you could get a sustained arc that would eat away at the conductors. I've seen pictures of the aftermath of service entrance electrical arcs; not pretty, and the fire department won't attempt to put out the fire until the power company comes to chop the supply....

That said: The only way that you can get your specific question answered, "Will the guts from a G3040MB1200CU fit properly in a G3030MB1200 enclosure?" is to ask the manufacturer. Not only do the size of the bus bars need to match, but the mounting holes on the back and the breaker positions on the front need to be the same.

There is a reasonable chance that they will match; the G3030 means 30 full sized slots with 30 circuits allowed, and G3040 means 30 full sized slots with 40 circuits allowed; this latter means that 10 of the slots will accept 'tandem' or 'skinny' breakers. So you are looking at two assemblies that are roughly the same size. Odds are that the replacement would work.

Failing that, you can buy panel retrofit kits that are designed specifically to fit in just about any panel; see for example http://www.cutlerhammer.com/unsecure/cms1/TD00308001E.PDF

Again, don't do this unless you can get the power chopped. Working 'hot' is a bad idea for a professional electrician. It is a form of probabilistic suicide for DIY.

-Jon
 
  #3  
Old 12-08-06, 08:08 AM
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Jon,

Thanks for the help. I should have been a bit clearer - this is definitely not something I would even attempt at doing without the power company pulling the meter. I've already contacted them to get all the information from them I need and to find out if this requires an inspection, and to give them some advance information on a time frame of when I want to do this. Trust me - I don't have a death wish! I've also got my dad helping me out, who was an electrician in a past life.

Thanks for the link on the refit kits, I'll give them a look. I've found a 3040 box at Lowe's, I think I'm going to stop by and take some measurements on the bus arrangement and attachment locations to see if it will fit also.

Any ideas on how or why the power tabs are getting eaten away? The box is in an attached garage, unheated but fully insulated. It stays fairly warm in the winter, as the furnace and water heater are also out there. The only thing I can figure out is possibly moisture during the seasonal changes. The kids like to leave the garage door open on the first nice days, and as soon as it is, we've got a nice moisture film on everything metal. But some of the tabs are 3/4 of the way gone.

Thanks for the help!
 
  #4  
Old 12-08-06, 09:24 AM
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Once the bus bars start to erode, then its all down hill. The erosion causes bad electrical contact, and then the current flowing through that bad electrical contact causes further erosion. I don't know why your panel started to erode in the first place; moisture could be an issue. Is the panel directly mounted to a concrete or block wall, which could keep the back of the panel cold for a while and cause condensation?

It is possible that your panel started out with bad breaker to bus bar connections, caused by mismatched breakers or some other problem.

Whatever the case, when you replace your panel, you should also replace the breakers. If the breaker contacts are eroded, then they will destroy the bus stabs in short order.

-Jon
 
  #5  
Old 12-08-06, 09:36 AM
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It's attached between the wall studs on the outside wall, not to a block wall or anything. There is only the pink insulation board then siding between the back of the box and the outside.

I had also planned on replacing all the breakers in the box for peace of mind. And now that you mention it, I do have a couple breakers that are a different make than the others, and one of these is attached to one of the bus bar tabs that is almost gone. It's possible they aren't compatible with the box. This was a house we moved into, so it was pre-existing.

I just can't believe and consider myself extremely lucky that this never caused a fire. The way I found out about it was when I was in the garage and actually heard the arcing going on inside the box.

Thanks!
 
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