Meter/Panel Combo question

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mccayry

mccayry

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Tennessee
Im looking at a house that has a 150A service. The HO has a Siemens 200A meter/panel combo he wants to install. The combo panel is equipped with feed through lugs so my thoughts were to install the meter/panel and feed throught to the existing 150A panel located inside. My question is do I consider the existing panel a subpanel and if so should the nuetral and ground be isolated? In the existing panel the grounds and grounded conductors are all terminated together so I would need to separate them.
 
Note also that in most situations the AHJ will want any grounding electrode conductors move to the service (outside) panel.
 
mccayry said:
Im looking at a house that has a 150A service. The HO has a Siemens 200A meter/panel combo he wants to install. The combo panel is equipped with feed through lugs so my thoughts were to install the meter/panel and feed throught to the existing 150A panel located inside. My question is do I consider the existing panel a subpanel and if so should the nuetral and ground be isolated? In the existing panel the grounds and grounded conductors are all terminated together so I would need to separate them.
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Are these feed through lugs protected by an OCPD?
 
The combo Panel has a 200A main breaker. I was planning on running 2/0 copper from the lugs on the meter combo to the line side of the 150A existing panel.
 
The 2/0 connecting from the lugs on the combo panel to the 150A existing panel is protected by the 200A main breaker on the combo panel. I hope that makes since.
 
mccayry said:
The 2/0 connecting from the lugs on the combo panel to the 150A existing panel is protected by the 200A main breaker on the combo panel. I hope that makes since.
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Got it, so you're sizing your #2/0 (200 amps) from Table 310.15(B)(6) {2008 NEC}.
 
mccayry said:
The combo Panel has a 200A main breaker. I was planning on running 2/0 copper from the lugs on the meter combo to the line side of the 150A existing panel.
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mccayry said:
The 2/0 connecting from the lugs on the combo panel to the 150A existing panel is protected by the 200A main breaker on the combo panel. I hope that makes since.
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infinity said:
Got it, so you're sizing your #2/0 (200 amps) from Table 310.15(B)(6) {2008 NEC}.
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310.15(B)(6) can not be used to determine size of these conductors if they are not carrying entire load of a dwelling.

IF the conductors are short enough you are allowed to use tap rules in 240.21. They will have to be in a raceway if using tap rules.
 
kwired said:
310.15(B)(6) can not be used to determine size of these conductors if they are not carrying entire load of a dwelling.

IF the conductors are short enough you are allowed to use tap rules in 240.21. They will have to be in a raceway if using tap rules.
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Do you not think 2/0 Copper is sufficient for feeding the 150A panel?
 
As long as he's using 2/0 to feed the main, then he's not required to use bigger conductors than that to feed the subpanel, even if the subpanel isn't serving the entire load of the house, correct?
 
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drive1968 said:
As long as he's using 2/0 to feed the main, then he's not required to use bigger conductors than that to feed the subpanel, even if the subpanel isn't serving the entire load of the house, correct?
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Nope, the meter main has a 200 amp OCPD protecting the feeder to the panel. If that feeder isn't carrying the entire load then the feeder conductors would need to be rate at a full 200 amps per 310.16. You can't use 310.15(B)(6) if the entire load is not fed from that feeder.
 
mccayry said:
Do you not think 2/0 Copper is sufficient for feeding the 150A panel?
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1/0 copper is sufficient to feed the 150 amp panel but it can not have 200 amp overcurrent device on the supply side unless it also satisfies the feeder tap rules.
 
drive1968 said:
As long as he's using 2/0 to feed the main, then he's not required to use bigger conductors than that to feed the subpanel, even if the subpanel isn't serving the entire load of the house, correct?
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infinity said:
Nope, the meter main has a 200 amp OCPD protecting the feeder to the panel. If that feeder isn't carrying the entire load then the feeder conductors would need to be rate at a full 200 amps per 310.16. You can't use 310.15(B)(6) if the entire load is not fed from that feeder.
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Rob, if the service entrance conductors to the combo panel are indeed 2/0 sized from 310.15(B)(6) and he feeds to the 150A panel inside, wouldn't 215.2(A)(3) allow the feeder to be the same size as the service conductors?
 
Little Bill said:
Rob, if the service entrance conductors to the combo panel are indeed 2/0 sized from 310.15(B)(6) and he feeds to the 150A panel inside, wouldn't 215.2(A)(3) allow the feeder to be the same size as the service conductors?
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IMO yes. Good point.
 
I know it is early and I may need more coffee but, if there is an OCPD- 200A and then feed to a 150A MB panel, why would you not be able to use 1/0 CU feed from the 200A to the 150A. Wouldn't the 150A MB protect the Feeder conductors?
 
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