size service entrance wires

[hubertyb00]

3, 200 amp panels with seperate meters. I know I run 2/0 to the meters from all of the panels, but what size, or how do I figure out what to run from the meter up the service mast.

 

[iwire]

Two ways to go.

1) Do load calculations and figure out the total combined calculated load.

2) Waste money and run 600 amps worth of conductors.

The NEC has some good examples of load calcs in the annex.

 

[LarryFine]

Two ways to go.

1) Do load calculations and figure out the total combined calculated load.

2) Waste money and run 600 amps worth of conductors.

I heartily recommend method #1.

 

[hubertyb00]

thanks alot for the advice. I agree option two would be just rediculous.

 

[LarryFine]

thanks alot for the advice.

You're welcome, and welcome to the forum, too! :smile:

 

[gotmud]

Now don't flame me but I always assumed you had to run a wire big enough to carry the max load of the main breaker in the panel??? So what your saying is if I put a 200 amp panel in a house with a caculated load of 125 amps I only have to run 125 amp wire up the riser on the line side of the meter? Umm I'm thinking I'd be back replacing that wire per MY inspector..

 

[mivey]

Now don't flame me but I always assumed you had to run a wire big enough to carry the max load of the main breaker in the panel??? So what your saying is if I put a 200 amp panel in a house with a caculated load of 125 amps I only have to run 125 amp wire up the riser on the line side of the meter? Umm I'm thinking I'd be back replacing that wire per MY inspector..

see 230.42

 

[hillbilly]

Now don't flame me but I always assumed you had to run a wire big enough to carry the max load of the main breaker in the panel??? So what your saying is if I put a 200 amp panel in a house with a caculated load of 125 amps I only have to run 125 amp wire up the riser on the line side of the meter? Umm I'm thinking I'd be back replacing that wire per MY inspector..

I believe the OP is talking about feeding 3 seperate 200A meters/service panels from a single utility drop.....how to size the service conductors from this drop to the point where the conductors are split off to each panel.

There is probably zero chance that any of the panels will be loaded to 200A, and certainly not at the same time....thus, the service drop will never see 600amps load.

On a drop to a single meter, I use table 310.15(B)(6) for residential, and for commercial, I size the conductors to carry the full amp rating of the main disconnect.
Others may do this differently.

For the OP's application, I would do load calculations to determine the total combined load on the conductors and size accordingly.

steve

 

[gotmud]

Ok yes i understand you can use 310.15b6 but in his case I would assume if your doing 1 service drop on 3-200 amp panels you would have to run either 1250's (which you would never do) or parallel 300's. You would have to make those riser wires rated to the full load....600 amps (give or take a few derate codes)...You coudn't do them at the calculated load of each panel and add them up...There is a possibility that those panels in the future COULD be loaded with more loads so you have to go off of the combined main breakers...or am I thinking wrong here? I've always been taught that your feeder wires have to match your main breaker(s) not just the caculated load...Also in 230.42 that MIVEY was telling me about, it states basically that the wire has to be large enough for the caculated load AND not less than the service disconnect...

 

[Twoskinsoneman]

Ok yes i understand you can use 310.15b6 but in his case I would assume if your doing 1 service drop on 3-200 amp panels you would have to run either 1250's (which you would never do) or parallel 300's. You would have to make those riser wires rated to the full load....600 amps (give or take a few derate codes)...You coudn't do them at the calculated load of each panel and add them up...There is a possibility that those panels in the future COULD be loaded with more loads so you have to go off of the combined main breakers...or am I thinking wrong here? I've always been taught that your feeder wires have to match your main breaker(s) not just the caculated load...Also in 230.42 that MIVEY was telling me about, it states basically that the wire has to be large enough for the caculated load AND not less than the service disconnect...

The NEC is based on practical safe guards... not absolute fail safes... you know what I mean. By unnormal, practically impossible circumstance, every circuit in a residence could be overloaded continuously and start burning up equipment that was not made to run at full load continuously....