100 Amp Service with a 200 Amp Panel

[Sam Morris]

When is it OK to have a 100 AMP service wires coming into a 200 AMP rated electrical panel ? House was only 1010 sq ft with all electrical appliances and with electric heat pump.

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[Trent Tarter]

It would only be allowed if there's an upstream main service disconnect switch rated at 100 amps.

[Jerry Peck]

When is it OK to have a 100 AMP service wires coming into a 200 AMP rated electrical panel ? House was only 1010 sq ft with all electrical appliances and with electric heat pump.

First, for clarification, this "200 AMP rated electrical panel" means:

a) that the panel rating is 200 amps (the panel bus rating, i.e., the panel is labeled as 200 amp mains), or,

b) that there is a disconnect in that panel and the disconnect overcurrent protection (fuses or breaker) is rated for 200 amps?

That difference is a very big difference.

Trent is correct is b) is the correct presumption.

If a) is the correct presumption, then you could feed a 200 amp panel with #12 AWG 20 amp rated conductor ... of course, though, you would only get 20 amps out of that 200 amp panel - and I am presuming that the #12 AWG is protected by 20 amp maximum overcurrent protection.

There is a c) presumption option: if the "service wires" are "service entrance conductors" which come from the meter and go to a service equipment panel where the service disconnect is, then there is no overcurrent device disconnect at the supply end of the service entrance conductors, making the only protection of the service entrance conductors being the downstream service disconnect.

If c) is the correct presumption, then ... NO ... 100 amp rated service entrance conductors are not allowed to feed a 200 amp service disconnect.

This question is an example of why correct terminology needs to be used, so the correct presumptions may be made to answer the question.

If the question had been: 'When is it OK to have a 100 AMP service entrance conductors coming into a 200 AMP rated service disconnect in the service equipment panel ?', then the answer would be a simple - '100 amp service entrance conductors are not allowed to feed a 200 amp service disconnect breaker'

[Sam Morris]

First, for clarification, this "200 AMP rated electrical panel" means:

a) that the panel rating is 200 amps (the panel bus rating, i.e., the panel is labeled as 200 amp mains), or,

b) that there is a disconnect in that panel and the disconnect overcurrent protection (fuses or breaker) is rated for 200 amps?

That difference is a very big difference.

Trent is correct is b) is the correct presumption.

If a) is the correct presumption, then you could feed a 200 amp panel with #12 AWG 20 amp rated conductor ... of course, though, you would only get 20 amps out of that 200 amp panel - and I am presuming that the #12 AWG is protected by 20 amp maximum overcurrent protection.

There is a c) presumption option: if the "service wires" are "service entrance conductors" which come from the meter and go to a service equipment panel where the service disconnect is, then there is no overcurrent device disconnect at the supply end of the service entrance conductors, making the only protection of the service entrance conductors being the downstream service disconnect.

If c) is the correct presumption, then ... NO ... 100 amp rated service entrance conductors are not allowed to feed a 200 amp service disconnect.

This question is an example of why correct terminology needs to be used, so the correct presumptions may be made to answer the question.

If the question had been: 'When is it OK to have a 100 AMP service entrance conductors coming into a 200 AMP rated service disconnect in the service equipment panel ?', then the answer would be a simple - '100 amp service entrance conductors are not allowed to feed a 200 amp service disconnect breaker'

There is No upstream 100 AMP OCPD installed, this is the only panel. This GE panel has a 200 AMP OCPD installed.

[Jerry Peck]

There is No upstream 100 AMP OCPD installed, this is the only panel. This GE panel has a 200 AMP OCPD installed.

Sam, then this is the answer ... presuming that these are service entrance conductors and service equipment:

If the question had been: 'When is it OK to have a 100 AMP service entrance conductors coming into a 200 AMP rated service disconnect in the service equipment panel ?', then the answer would be a simple - '100 amp service entrance conductors are not allowed to feed a 200 amp service disconnect breaker'