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measure_twice 10-13-2005 02:23 PM

Subpanel how to ?
Well i just finished my basement for an in-law apartment
i would like to add a subpanel so everything in the apartment is in its own panel. i have 100amp service and would like to feed a 100amp subpanel
is this possible? and if so how? or does the sub have to be lower amp (ex: 40a, 60a)?

You may ask why i think i need a 100A sub, my concern is that this apartment has a washer, dryer, range and double oven, as does my own living space.

:) What if we all decide to cook and do laundry at the same time?

K2eoj 10-13-2005 10:32 PM

Until someone comes along to answer your question here is a site I pulled of Contractor Talk That will help you determine your load. Some of the appliances, lights, get to be downrated because the NEC figures not everything will be used at once. I just sized a small duplex with a 100 amp service and came up with 108 amps after downrating. If I switch the dryer to gas I'll probably be ok. Here is the site.

BigA 10-14-2005 06:41 AM

I don't know of any inherent safety issues with having a subpanel the same size as your main panel - I'll let the guys who know the electrical codes answer that one. However, if you really think that both living spaces NEED 100A, then you really should do a load analysis of your house to see if you need to upgrade the service. It will be a major inconvenience if you keep blowing the main breaker just because you both decided to cook and do laundry at the same time.

Whatever you do, you should probably get a "Main Service Rated panel" which basically means that the panel has it's own breaker - its not required, because you already have a braker in YOUR main panel, but it will add to the convenience.

It also depends on what you are planning to do with the space. If you are planning to rent the place out I would seriously consider having an additional Main Service installed with a seperate Meter. If it is truly for "in-laws" or other guests, maybe this isn't necessary.

jbfan 10-14-2005 08:49 AM

You really need to have a load calculation done. What are you using to heat with and how are you heating your water? you can run a 100 amp sub from a 100 amp feed, but you will only have the protection of the 100 amp feed. Witout a load cal. you may be close to overloading your service. I sugesst you contact a licensed electrician for options.

measure_twice 10-15-2005 11:55 AM

Thanks for the info guys.

Heat and hot water run on oil.

i was planning on upgrading the service to 200Amps in the spring anyway when i build a work shop in the back yard 20'X24'.

But we just bought the house 4 months ago and since we just renovated the lower and up levels you can imagine how tight the money has gotten.

A service upgrade at this point just isn't within the budget

Whats the simplest way to do a load analysis?

K2eoj 10-15-2005 01:23 PM


Whats the simplest way to do a load analysis?

Were you able to find the site i posted. I was able to do a load calc so it must be pretty simple.

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