main lug box instead of main breaker box?


Old 07-08-06, 11:29 AM
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Red face main lug box instead of main breaker box?

My house currently has an OLD main breaker box from the 1960's. It is a "main lug" box and the sticker says it is a 200 amp panel. It has no main breaker. It's door is falling off. It has big 240v circuits on the top, then a 60a breaker "main for lights" leading to 20 amp 120v circuits below. It has no empty slots for additional circuits. The condition looks old. I need to add a few new circuits, and rather than add a subpanel, I want to replace it with a new 200amp 20/40 box which will have more than enough room for my requirements.

Here's my question. Why would they have used a main box without a main breaker? The 240v breakers include a 100amp for an electric furnace (which is not used anymore...), a 60 amp for an stove/oven, a 30 amp for water heater, a 50 amp for clothers dryer, and a 30 amp for A/C unit. Then, like I said, there's a 60 amp "main for lights" from which all other circuits are run.

Is it possible that all these large amp applicances would constantly trip a 200 amp main so that's why they didn't use one initially? I WANT to use a new box with a main breaker... seems safer to me. Since we don't use the electric furnace anymore, I may not even include that circuit at all when I put the new main box.

So what do you think? Should a 200amp "main breaker" box be OK, or do I use a "main lug" style like originally used?

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Old 07-08-06, 11:46 AM
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Originally Posted by PNerd

So what do you think? Should a 200amp "main breaker" box be OK, or do I use a "main lug" style like originally used?

Well you should use a main breaker style panel. Actually you are going to have to unless you have a main disconnect before this. It is a code requirement. In either case, the first disconnect is your service equipment and needs to follow the proper grounding/bonding rules in the install.

If you have a disconnect in/on the house other than the panel, then you could use an MLO panel.

Be sure the conductors feeding the panel are large enough to handle the rating of the main breaker in the main panel.
Old 07-08-06, 11:50 AM
Join Date: Mar 2006
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You have what is called a "split-bus" panel. These were once common. The NEC requirement is that all power must be disconnected with no more than six hand movements and the split-bus panels had spaces for a maximum of six 2-pole (240 volt) breakers with handle ties. That meant a maximum of five 240 volt circuits plus the 60 amp "main" for all of the 120 volt circuits on the lower bus.

Yes, you want to use a "main breaker" panel. Your local code may even require it.

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