Subpanel Questions

[Beemer]

I am considering having a subpanel about 90 feet from our main panel for (residential) 2 lighting circuits, 2 outlet circuits and a baseboard heat unit to avoid running all the wires back tot he main panel.
I see that 100 amp panels are the smallest allowed, what wires would be needed ?
Is there a wire type that can be installed exposed in the wood framing in the unfinished basement ceiling area?
If not, would it be individual wires installed in EMT running in the framing?
Being that I don't see needing the 100 amp capacity of the minimum panel size, can the wire sizes be reduced using lesser breakers in the main panel for the subpanel wire protection?

 

[sparky 1971]

I am considering having a subpanel about 90 feet from our main panel for (residential) 2 lighting circuits, 2 outlet circuits and a baseboard heat unit to avoid running all the wires back tot he main panel.
I see that 100 amp panels are the smallest allowed, what wires would be needed ?

100 amps is the minimum service size. You can install whatever size feeder for a sub you want. If you truly want to go with 100 amps, #1 aluminum, but easier would be #2 and use a 90 amp breaker. For no more than what you have, 50 or 60 amps would be plenty.

Is there a wire type that can be installed exposed in the wood framing in the unfinished basement ceiling area?

Romex or SER cable, unless there is an amendment disallowing it. We can do it here as long as we run within 12" of a wall when running through holes and are secured in the upper half of a joist when running along side it. #2 SER cable for the 90 amp circuit. 6/3 Romex (copper) will get you 50 amps, but the inspectors here let us put it on a 60.

If not, would it be individual wires installed in EMT running in the framing?

If you're using EMT, you can on the framing. Running it through (in) the framing is a pain.

Being that I don't see needing the 100 amp capacity of the minimum panel size, can the wire sizes be reduced using lesser breakers in the main panel for the subpanel wire protection?

You don't have to get a 100 amp main breaker panel if it's in the same building. Main lug is fine. You can get a 6 space 12 circuit panel on the cheap, but an 8, 12 or 16 space will be just a little more

 

[Beemer]

Thanks for the reply.

If understand correctly, if I had a subpanel that has a 100 amp main breaker it's alright to reduce it's capacity by adjusting the wire size and breaker installed in the main panel. Is that right?
Is that type of panel allowed for a subpanel?

You wrote "You can get a 6 space 12 circuit panel on the cheap, but an 8, 12 or 16 space will be just a little more".
Is that a panel without a main breaker?

For the full 100 amps, what would the copper wire size needed be (vs aluminum)?

Is there a specific ground wire gage required?

 

[sparky 1971]

Thanks for the reply.

If understand correctly, if I had a subpanel that has a 100 amp main breaker it's alright to reduce it's capacity by adjusting the wire size and breaker installed in the main panel. Is that right?

Yes. You can have whatever size you'd like as long as the feeder wire is protected by the appropriate sized breaker.

You wrote "You can get a 6 space 12 circuit panel on the cheap, but an 8, 12 or 16 space will be just a little more".
Is that a panel without a primary breaker?

Yes

For the full 100 amps, what would the copper wire size needed be (vs aluminum)?

#3.

Is there a specific ground wire gage required?

#10 for 50 or 60 amps, #8 for 100. If you use EMT, the pipe can be the ground. Romex or SER cable will already have the right sized ground.

 

[75gmck25]

Start out by looking at your existing main panel, since it's usually easier to stay with the same brand so that breakers interchange. Then do an online search for 100 amp panels of that brand. Pick the one you like, preferably something like an 8, 12 or 16 since it gives you better flexibility. I would usually pick a main breaker sub-panel, since there seems to be more available, but that's your choice.

I used a 16 space main breaker Square D QO sub-panel, but the feeder from the main to sub panel has only a 60 amp breaker. I did run 2-2-2-4 AL MHF, but at this point don't have any need to use the max allowed 90 amp breaker.

AL MHF is used in a lot of applications, so it's relatively cheap compared to other choices. Don't get AL SER and AL MHF confused with the stories about older homes that use aluminum wiring for normal receptacles. AL is widely used for SER wiring, and new panels are set up to terminate it properly. Copper is generally much more expensive.

MHF can be direct bury, but I used 2" conduit from the house to the detached garage. Once you get the trench dug, it's not much more work to drop in conduit and connected to the panels, although it gets expensive for a long distance run. If you use conduit, make sure you add a pull string just in case you find you need to later pull more/new wiring.

 

[Beemer]

Start out by looking at your existing main panel, since it's usually easier to stay with the same brand so that breakers interchange. Then do an online search for 100 amp panels of that brand. Pick the one you like, preferably something like an 8, 12 or 16 since it gives you better flexibility. I would usually pick a main breaker sub-panel, since there seems to be more available, but that's your choice.

I used a 16 space main breaker Square D QO sub-panel, but the feeder from the main to sub panel has only a 60 amp breaker. I did run 2-2-2-4 AL MHF, but at this point don't have any need to use the max allowed 90 amp breaker.

AL MHF is used in a lot of applications, so it's relatively cheap compared to other choices. Don't get AL SER and AL MHF confused with the stories about older homes that use aluminum wiring for normal receptacles. AL is widely used for SER wiring, and new panels are set up to terminate it properly. Copper is generally much more expensive.

MHF can be direct bury, but I used 2" conduit from the house to the detached garage. Once you get the trench dug, it's not much more work to drop in conduit and connected to the panels, although it gets expensive for a long distance run. If you use conduit, make sure you add a pull string just in case you find you need to later pull more/new wiring.

Thanks for the reply.
My situation is everything is all in the same residence, no detached structure and nothing to get buried.
I think Dad has a 100 amp Square D panel in storage but that doesn't match the main panel, but the price is right including all the breakers.
He was an old time electrician and put the fear of god in me in regards to aluminum wiring. That's a hurdle.

 

[Beemer]

I have a related question regarding how to account for the amperage of a 220 baseboard heater.
Being 220 it will take a three wire cable and double pole breaker in the subpanel, but how is the amperage accounted for in the overall load?
If the heater notes 8 amps in the specs, does that put a load of 8 amps on each leg of the double pole breaker, needing 16 amps in the subpanel and the feed from and breakers in the main panel?

Edit; 240 volt; 220 was typo

 

[Norcal]

Fear of god in regards to aluminum wiring? So your dad taught you ignorance of aluminum conductors and what voltages are used in the US. Properly installed Aluminum alloy conductors are just fine, they provide a safe, reliable, economical, installation. The wild west sh*t show in the 1960's with 10, & 12 AWG aluminum conductors was the fault of UL, & Kaiser Aluminum, because of a lack of ANY standards for that **** in the 1960's. It's because of that debacle I have no respect for UL.

 

[sparky 1971]

I have a related question regarding how to account for the amperage of a 220 baseboard heater.
Being 220 it will take a three wire cable and double pole breaker in the subpanel, but how is the amperage accounted for in the overall load?
If the heater notes 8 amps in the specs, does that put a load of 8 amps on each leg of the double pole breaker, needing 16 amps in the subpanel and the feed from and breakers in the main panel?

Wattage ÷ 240 = amperage. Take that X 1.25 to size the circuit. EX: 1500 watt heater ÷240 = 6.25 amps. 6.25 X 1.25= 7.8. You could use #14 wire and a 15 amp breaker or 12's and a 20. If it's only one heater, you will be fine with the 20 amp circuit for sure, probably the 15 amp circuit. I've never seen one more than 2000 wattsbut maybe there is such a monster.

And you will be fine with the aluminum wire of today.

 

[Beemer]

Wattage ÷ 240 = amperage. Take that X 1.25 to size the circuit. EX: 1500 watt heater ÷240 = 6.25 amps. 6.25 X 1.25= 7.8. You could use #14 wire and a 15 amp breaker or 12's and a 20. If it's only one heater, you will be fine with the 20 amp circuit for sure, probably the 15 amp circuit. I've never seen one more than 2000 wattsbut maybe there is such a monster.

And you will be fine with the aluminum wire of today.

I didn't express the misunderstanding well.
The question is about the efffect of the heater in the subpanel's total sum of loads.
What I am stumbling on is tabulating the sum of amps in the panel contributed by the 240 heater; The 2 hot wires (3 wire plus ground) is causing the confusion.
In your example, (1500/240) x 1.5 - 7.8 amps. Is that on each of the hot lines so the subpanel needs to accomodate 2 x 7.8 amps for the heater in adding up the total loads on the subpanel?

 

[The Cobbler]

will take a three wire cable

just to clarify, for building wire , you need 2 wire plus ground. 3 wire would indicate 3 wire plus ground .

 

[Beemer]

Fear of god in regards to aluminum wiring? So your dad taught you ignorance of aluminum conductors and what voltages are used in the US. Properly installed Aluminum alloy conductors are just fine, they provide a safe, reliable, economical, installation. The wild west sh*t show in the 1960's with 10, & 12 AWG aluminum conductors was the fault of UL, & Kaiser Aluminum, because of a lack of ANY standards for that **** in the 1960's. It's because of that debacle I have no respect for UL.

You wrote yourself that there were issues with aluminum conductors.
Your response in an offending manner is not appreciated.

 

[Beemer]

just to clarify, for building wire , you need 2 wire plus ground. 3 wire would indicate 3 wire plus ground .

Right, just wrong terminology used. I am thinking in terms of Romex so the ground is in there and I tend to not count it in describing.
By 3 wire I meant 2 hots and a neutral, and ground is there as you pointed out.

 

[sparky 1971]

I didn't express the misunderstanding well.
The question is about the efffect of the heater in the subpanel's total sum of loads.
What I am stumbling on is tabulating the sum of amps in the panel contributed by the 240 heater; The 2 hot wires (3 wire plus ground) is causing the confusion.
In your example, (1500/240) x 1.5 - 7.8 amps. Is that on each of the hot lines so the subpanel needs to accomodate 2 x 7.8 amps for the heater in adding up the total loads on the subpanel?

It's 7.8 amps total. You are putting way too much thought into this. Don't worry about it. Any sub panel from 50 amps on up is going to be more than enough. You could probably get by with a 30, but that would be stupid.

Right, just wrong terminology used. I am thinking in terms of Romex so the ground is in there and I tend to not count it in describing.
By 3 wire I meant 2 hots and a neutral, and ground is there as you pointed out.

There will be no neutral for a baseboard heater. 240 is two hots and a ground. 120/240 is two hots, neutral, and a ground. The only things I can think of off hand in a residential setting are: Range, dryer, a large camper, a subpanel, and the service.

 

[sparky 1971]

You wrote yourself that there were issues with aluminum conductors.
Your response in an offending manner is not appreciated.

Once upon a time there were issues with aluminum wires. Those issues have been taken care of and the aluminum of today is fine. You have aluminum feeding your house from the POCO, everyone does. I ran my own aluminum underground to the house and garage, ran a #2 SER feeder to a sub panel and never once did I second guess it. I've installed countless feet of aluminum on jobs and am not concerned one bit even though I would be the first on on the naughty list if there were a problem.

 

[Beemer]

Thanks sparky.

 

[wyliesdiesels]

Thanks for the reply.
My situation is everything is all in the same residence, no detached structure and nothing to get buried.
I think Dad has a 100 amp Square D panel in storage but that doesn't match the main panel, but the price is right including all the breakers.
He was an old time electrician and put the fear of god in me in regards to aluminum wiring. That's a hurdle.

youre applying fears about the old aluminum alloys to the new ones. you cant compare the 2. there is absolutely nothing wrong with the current aluminum alloys used for building wire.

read the info on pg 2 in the link below

http://www.salesmanagementplus.com/ContentOnDemand/MfgContentPieces/Images2/Southwire/AlumaFlexSIMpullTHHNBrochure.pdf

 

[wyliesdiesels]

You wrote yourself that there were issues with aluminum conductors.
Your response in an offending manner is not appreciated.

the issues were with the OLD ALLOYS that havent been used in decades... time to get caught up on current wiring... read page 2 in link above

 

[Beemer]

I found a loop of 6/3+gr copper romex stored in the attic that would reach about half the distance needed to the subpanel.
Is there any code issue splicing the feed wires in a box out on the run in the unfinished ceiling space of the basement to make the full length needed?

 

[dave*99]

I found a loop of 6/3+gr copper romex stored in the attic that would reach about half the distance needed to the subpanel.
Is there any code issue splicing the feed wires in a box out on the run in the unfinished ceiling space of the basement to make the full length needed?

Is the Romex NM or NM-B?

 

[Norcal]

Is the Romex NM or NM-B?

If it is old enough to be just marked NM, it is scrap metal, the NEC requires 90°C conductors in NM sheathed cables, which are marked as NM-B.

 

[alfredeneuman]

The entire utility grid is wired with aluminum.
That was the first alloy that got used, but ended up being too stiff and brittle for general use.
The alloys of today are a different thing entirely (softer, easier to bend)
Your paranoia is unwarranted.

 

[Beemer]

The entire utility grid is wired with aluminum.
That was the first alloy that got used, but ended up being too stiff and brittle for general use.
The alloys of today are a different thing entirely (softer, easier to bend)
Your paranoia is unwarranted.

Not thinking on that right now.
I have about 60 feet of the copper that I prefer not taking to recycling.

 

[Beemer]

Is the Romex NM or NM-B?

NM-B

 

[mike93lx]

NM-B

Then it's good to use. You can splice it, just have to keep that box accessible, as you noted.

If you change wire size at the splice, your breaker feeding it needs to be sized to the smaller wire (you can always breaker at smaller than that, just not bigger). Get a big junction box though. #6 isn't all that easy to work with