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Old 06-16-2012, 12:37 AM   #1
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service entrance sizing


Hi,
on a rental next to me, i have two units connected by a roofed breezway. Each house has a new 125A subpanel and we are in the process of replacing the dated meter panel in the front house where both meters are located.

We have purcahsed a new Square D dual meter base and disconnect to replace the existing, but dated two meters and rustic disconnects. The question that i need help with is sizing the the conductors for the service drop (Meter to masthead). Given that we have two 125am services, should i size the drop to 250A? If so, this gives 4/0 conductors right?

Also,how do i calculate the size of conduit where teh 4/0 conductors will go from meterbase to masthead.

many thanks, Steve.

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Old 06-16-2012, 07:06 AM   #2
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service entrance sizing


SIze it based on the calculated load. It probabely does not have to be full sized. There is an optional calculation in ARt 220 for two family dwellings. Can you do electrical work on a dwelling you do not live in where you live? You may want to look into that. Also, 4/0 AL is only rated for 200A when supplying the total load of a dwelling unit.

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Old 06-16-2012, 07:35 AM   #3
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service entrance sizing


Quote:
Originally Posted by Steve Burke View Post
Hi,
on a rental next to me, i have two units connected by a roofed breezway. Each house has a new 125A subpanel and we are in the process of replacing the dated meter panel in the front house where both meters are located.

We have purcahsed a new Square D dual meter base and disconnect to replace the existing, but dated two meters and rustic disconnects. The question that i need help with is sizing the the conductors for the service drop (Meter to masthead). Given that we have two 125am services, should i size the drop to 250A? If so, this gives 4/0 conductors right?

Also,how do i calculate the size of conduit where teh 4/0 conductors will go from meterbase to masthead.

many thanks, Steve.
Is the utility involved to shut off the power while you swap the meter base? Sounds like you may be trying to do this with live feed/drop from pole. Maybe I'm just being paranoid but this isn't a place to go MacGyver on. There isn't a lot of protection to you upstream of a 4/0 drop.
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Old 06-17-2012, 02:28 PM   #4
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service entrance sizing


The calculated load for the front house is 115amps and the calculated load for the back house is 95amps. Both "houses" are joined by a roofed breezeway.

The service entrance, 2 meters, will be located on the front house and each house will have a main disconnect at 125A at the meter.

Given the combined load of 215amps, we are planning to use 3/0 copper for the service entrance with a 2" mast. This seems a bit excessive since all appliances in both "houses" will not operate concurrently.

Does anyone have a different way of looking at the load and conductor sizing requirements?

Separately, we are planning to run a 1 1/4" mast for incoming cable and phone. The plan is to run both cable and telephone through a single mast that will be at least 12" away from power. Anyone see an issue with this arrangement?
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Old 06-17-2012, 02:34 PM   #5
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service entrance sizing


Quote:
Originally Posted by Steve Burke
The calculated load for the front house is 115amps and the calculated load for the back house is 95amps. Both "houses" are joined by a roofed breezeway.

The service entrance, 2 meters, will be located on the front house and each house will have a main disconnect at 125A at the meter.

Given the combined load of 215amps, we are planning to use 3/0 copper for the service entrance with a 2" mast. This seems a bit excessive since all appliances in both "houses" will not operate concurrently.

Does anyone have a different way of looking at the load and conductor sizing requirements?

Separately, we are planning to run a 1 1/4" mast for incoming cable and phone. The plan is to run both cable and telephone through a single mast that will be at least 12" away from power. Anyone see an issue with this arrangement?
There is an optional method for two family dwellings in Article 220. You may be able to get to a 200a service that way. What is the total sq. footage? Nameplate of all appliances? HVAC?
__________________
All responses based on the 2011 NEC.
If you live in New Jersey click here. All other states click here.
Please check with local, county and state officials as laws may vary.
Sizing motors here. Online motor calculator here. Online calculators here.
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Old 06-17-2012, 03:09 PM   #6
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service entrance sizing


thanks Electures, i will look up the alternative you mentioned.

Regarding
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QUESTION by electures
What is the total sq. footage? Nameplate of all appliances? HVAC?
The square footsage of the front house is just shy of 1000sq ft and the back house is 900. Both houses have gas hot water, gas heat (no blower, wall furnace and a floor furnace) and gas stoves/ranges.

For the load calc, i used the amperage from the nameplate for each appliance.
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Old 06-17-2012, 05:32 PM   #7
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service entrance sizing


Quote:
Originally Posted by Steve Burke View Post
thanks Electures, i will look up the alternative you mentioned.

Regarding

The square footsage of the front house is just shy of 1000sq ft and the back house is 900. Both houses have gas hot water, gas heat (no blower, wall furnace and a floor furnace) and gas stoves/ranges.

For the load calc, i used the amperage from the nameplate for each appliance.
What are the specific appliances? Any A/C, D/W, GD, fans, motors, pumps?

Using the standard method, your general lighting load is 47.5A total for both units. Add the remaining loads and see what it adds up to.

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All responses based on the 2011 NEC.
If you live in New Jersey click here. All other states click here.
Please check with local, county and state officials as laws may vary.
Sizing motors here. Online motor calculator here. Online calculators here.
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