Looking for an opinion on service entrance

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I'm an electrical engineer but not an electrician, hope I can still post here.

I'm working on planning out an upgrade to a 2 family that I own. Currently 2x100A service (single 4/0-4/0-4/0 Alum. SEU, dual pan).

Would like to go to 2x200A panels. I assumed this meant a 400A capable SE to the (new) dual meter pan, which using residential table means 400MCM copper or 600MCM aluminum. Then I saw something mentioned about only sizing the SE to the calculated load and not to the main breakers themselves, but that makes no sense to me. My understanding was the SE must always be sized to the sum of the main breakers, but wondering if there is something different since its two meters and two distinct units? I think what I read was incorrect or not clearly stated, and that they meant to say to size both the mains and the SE to the calculated load, but was curious for confirmation. I'm aware the POCO does their own calc and their aerials will likely be 1-2 sizes smaller than my SE but wondering about my portion of it.

It actually looks like my POCO will require a significant payment to do 400A service, so I'm considering a somewhat non-standard 2x150 instead as that falls under their "we'll pay for it" limit and would save me money on the SE as well, but still thinking it through. A very generous load calc with lots of buffer only puts them at about 110-125A peak load each and technically the dwelling is still served by 200A or greater service which seems to be what most authorities want these days.

An aside question - code clearly requires each unit to have access to their main disconnect, which is fine, each will have the panel in their unit (they actually don't now), but I saw mention that for multi-dwelling, that all disconnects go in one place, meaning at the meter and wiring the panels as subs. Wasn't sure if this was a code requirement or just a locality thing. Most 2-fams around here don't have disconnect at the meter. I understand the benefit of doing it that way for a fire or other emergency, just wondering if its actually required.

I'm going to run this by POCO and inspector when the time comes but I like to have a clear view in my head before relying on their sometimes assinine requirements/recommendations. Thanks for any thoughts/input.
 

jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
As an engineer you may ask design questions. But, if you are the installer (i.e. a DIY) we can not answer "how-to" questions.

Will you be hiring an electrical contractor for this project?
 
YOu can post here, & welcome to the forum.... but being its a 2 family home I doubt you can do the work. Not sure if you were planning on it or not.

I live in one of the units so I can do my own work (it will be a total renovation). My town prefers to tell you that MA state law doesn't allow you to do any electrical work, but that isn't the case and at very least I will do all the branch wiring whether they like it or not, I'm good at digging in my heels until they just let me do it. If I have to hire out the SE, I will, but technically there is no law preventing me from doing it. If it passes inspection and follows the rules, they should not care IMHO. But enough of that rant. I didn't mention either way because I'm aware that for legal reasons nobody here wants to risk their posts being interpreted as binding or as a replacement for an inspector. So I will try to keep my discussions to a clearly design or best-practices nature :)

I'm well versed in electricity, just not always every single portion of the code or what the "norm" or "standard" is, thus input from experts that aren't trying to get the top $$ out of me is invaluable and much appreciated.
 
Your bio states electrical and data engineer.
From your questions, it would seem that you do more data then electrical work.

The NEC has an online version of the NEC. Your local building department can give you information about the local codes. The POCO will provide you either online layout, or in booklet form the requirements necessary for the layout of the type of service you are trying to install.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
In a service with a grouped main disconnect, there is no requirement that the service entrance conductors be rated for the sum of the service disconnects. The service entrance conductors only have to be rated for the full calculated load. Doesn't seem safe, I know, but code doesn't require it. I do, however, think it is a very good design (especially in residential where each unit is autonomous and tends to have handyman upgrades) to make the service entrance and meter pan be rated for the sum of the disconnects. I'd give maybe on a 5 unit facility and want maybe a 400A service for 5 units of 100A as long as it calculates to well under 400A. But with only two units, you can quickly run out of margin if someone decides to add a hot tub or switch a gas appliance to electric.

I think your plan of having two 150A main panels is fine. But you'll still need a 400A meter base if 200A won't handle the whole service. Did you do your load calculations per the standard or optional methods? What are those values (each unit and the total service) without adding any "buffers"?
 
Absolutely correct. I am datacom by profession and electrical by schooling, but obviously a degree in electrical engineering is much more concept than practice, hence asking questions. I've done a lot of research, and have plenty more to do, but obviously some things are very much open to interpretation. I have the POCO book (national grid) and for the most part they seem to discourage 400A service and lay out lots of additional requirements for it. Obviously once I speak with the local engineer I'll have a much better idea of what they can/can't do, I just want to go into it knowing as much as I can.

Your bio states electrical and data engineer.
From your questions, it would seem that you do more data then electrical work.

The NEC has an online version of the NEC. Your local building department can give you information about the local codes. The POCO will provide you either online layout, or in booklet form the requirements necessary for the layout of the type of service you are trying to install.
 
To clarify what you mean by "grouped main disconnect", my original intent was that the only mains be the ones in the two panels in the two different units, nothing before or after the meter outside (panel will be back to back with entrance), unless of course there is a requirement to have the meter mains due to 2 family which I'm still trying to figure out for sure. So with the only disconnects being the main breakers inside, it's valid to size based on calculated load? Interesting.

I ran a quick standard calc, so in theory the optional should be a bit lower, but because I haven't picked out/purchased the exact fridge, A/C, disposal, dishwasher, furnace, etc I just used some higher end estimates, rounded up on the SQFT, and tossed in a few extra 20A small appliance ckts too just to be safe. No, not exactly scientific but in the absence of exacts, I'd rather be high than low. One unit is about 110 and the other is about 125 (partially finished basement). In reality when I've got some better numbers both will likely calc out in the 80-100 range, so definitely 200 wouldn't be enough.

The dual meter bases (I can get them in both 300 and 400) seem much less cumbersome than the single 320/400 and aren't too expensive, so that's not a big deal. I think regardless I'd just do a 2x200/400 bus pan.

In a service with a grouped main disconnect, there is no requirement that the service entrance conductors be rated for the sum of the service disconnects. The service entrance conductors only have to be rated for the full calculated load. Doesn't seem safe, I know, but code doesn't require it. I do, however, think it is a very good design (especially in residential where each unit is autonomous and tends to have handyman upgrades) to make the service entrance and meter pan be rated for the sum of the disconnects. I'd give maybe on a 5 unit facility and want maybe a 400A service for 5 units of 100A as long as it calculates to well under 400A. But with only two units, you can quickly run out of margin if someone decides to add a hot tub or switch a gas appliance to electric.

I think your plan of having two 150A main panels is fine. But you'll still need a 400A meter base if 200A won't handle the whole service. Did you do your load calculations per the standard or optional methods? What are those values (each unit and the total service) without adding any "buffers"?
 
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tkb

Senior Member
Location
MA
I live in one of the units so I can do my own work (it will be a total renovation). My town prefers to tell you that MA state law doesn't allow you to do any electrical work, but that isn't the case and at very least I will do all the branch wiring whether they like it or not, I'm good at digging in my heels until they just let me do it. If I have to hire out the SE, I will, but technically there is no law preventing me from doing it. If it passes inspection and follows the rules, they should not care IMHO. But enough of that rant. I didn't mention either way because I'm aware that for legal reasons nobody here wants to risk their posts being interpreted as binding or as a replacement for an inspector. So I will try to keep my discussions to a clearly design or best-practices nature :)

I'm well versed in electricity, just not always every single portion of the code or what the "norm" or "standard" is, thus input from experts that aren't trying to get the top $$ out of me is invaluable and much appreciated.

I believe that in MA that is true of single family units only.
You cannot do your own work in a multi family building.
This would include the branch wiring also.
 
I believe that in MA that is true of single family units only.
You cannot do your own work in a multi family building.
This would include the branch wiring also.

It is a point of contention and seems to differ by locality. My town says for building permits, owner occupied 2-fam is fine. For electrical they say "state law prohibits owner electrical work regardless of dwelling", however that isn't true, in fact the only state law I've ever seen on the topic only mentions for-hire work. If they want to discourage people from getting a permit to do electrical work, that is their own problem, I guarantee you the average handyman is NOT hiring an electrician to swap receptacle or even run a new one, and in a lot of cases, much much more than that. But that's another discussion entirely which I'm sure would yield any number of opinions.

For the purpose of this discussion and to avoid any debate, I'm solely planning and designing, there is no actual work currently being performed.
 

electricmanscott

Senior Member
Location
Boston, MA
I believe you are correct that the law specifically spells out doing work "for hire" as to when you must get a permit.

At least that was the case and I am not sure if it still is.

Technically by the letter of the law I could wire a Wal Mart for free and not get a permit.

I know of towns that will not issue a permit to a homeowner regardless of the situation. I don't know that they have the right to refuse but refuse they do.
 
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Do you really think you need 200 amps to each unit? :confused:

Probably not, it's the default next step for single fam, so my mind sort of just automatically stepped to that, and it never hurts to have plenty of growth room. But obviously, it may be unreasonable in this case based on the necessary hardware. 100 isn't enough, 150 is probably enough, 200 is nice to have. But POCO is looking for "as much as we can make money off" so, such is life.
 

iwire

Moderator
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Location
Massachusetts
I believe that in MA that is true of single family units only.
You cannot do your own work in a multi family building.
This would include the branch wiring also.

Tim, the way the law is currently written in MA you can wire the Prudential Center without a license as long as you do it for free. I do know that each City and Town in MA handles it differently but here is the state law.


TITLE XX. PUBLIC SAFETY AND GOOD ORDER


CHAPTER 141. SUPERVISION OF ELECTRICIANS


Chapter 141: Section 1A. Licensure requirement; exceptions


Section 1A. No person, firm or corporation shall enter into, engage in, or work at the business or occupation of installing wires, conduits, apparatus, devices, fixtures, or other appliances for carrying or using electricity for light, heat, power, fire warning or security system purposes, unless such person, firm or corporation shall be licensed by the state examiners of electricians in accordance with this chapter and, with respect to security systems, unless such person, firm or corporation shall also be licensed by the commissioner of public safety in accordance with the provisions of sections fifty-seven to sixty-one, inclusive, of chapter one hundred and forty-seven.

This chapter shall not apply to: a person not engaged in the business described in this section who employs or contracts for the services of a person, firm or corporation engaged in such business; or to an apprentice employed by a person, firm or corporation licensed in accordance with this chapter; or to an agent, employee or assistant of a person, firm or corporation licensed in accordance with this chapter who does not engage in or perform the actual work described in this section.

If I do it for free I did not "engage in, or work at the business or occupation of installing wires,.........."
 

tkb

Senior Member
Location
MA
Tim, the way the law is currently written in MA you can wire the Prudential Center without a license as long as you do it for free. I do know that each City and Town in MA handles it differently but here is the state law.




If I do it for free I did not "engage in, or work at the business or occupation of installing wires,.........."

I only found the sections that you refered to also.
I thought I read somewhere about the homeowner permits.
Must be one of those things that gets discussed in the code update classes that we assume is law.

But the OP will have not be able to do his own service and get connected by the POCO without a permit from his town.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
To clarify what you mean by "grouped main disconnect", my original intent was that the only mains be the ones in the two panels in the two different units, nothing before or after the meter outside (panel will be back to back with entrance), unless of course there is a requirement to have the meter mains due to 2 family which I'm still trying to figure out for sure. So with the only disconnects being the main breakers inside, it's valid to size based on calculated load? Interesting.

You can probably have a main breaker panel only in each unit by using 230.40 exception 1. So what you'll have is multiple sets of service entrance conductors (SECs), one to each occupany, and it looks like each set will have one main breaker disconnect. Be aware of the length limit for SECs inside a building before you hit the main, as each area has its own rules (NEC says 0 feet, WA state is 15', don't know about Mass). That rule could mandate that the disconencts be outside. Next, see 230.71 (I haven't done any multifamily work and find the wording here confusing. I think because you're using 230.40 ex 1, you don't have a limit of 6 disconnects for the service, just 6 per set with no limit on the number of SEC sets).

Whether the service disconnects are grouped or not, you still don't size the service by adding the mains on those disconnects. If you have two units, and each has a calculated load of 125A, that does not mean your service need to be 250A. You do it a new calculation taking all the items in both units and doing one load calculation with all of that (e.g. two furnaces, 4 kitchen appliance circuits, two dishwashers...). This causes the part of the equation where you take 100% of the load to be applied only once instead of twice. You may also get to take advantage of the 75% demand factor for fastened-in-place appliances because you'll most likely have 4 or more of them, whereas in a single unit you may not reach four. Make sure you see all the exclusions though in 220.53.
 
Another good one (my emphasis added), no permit required :) I'm perfectly fine pulling a permit, if they won't allow it, there will be a battle.

If I can find a sparky willing to pull the permit and do a final look-over for a reasonable fee (while allowing me to do the labor), I may consider that.

No person shall install for hire any electrical wiring or fixtures subject to this section without first or within five days after commencing the work giving notice to the inspector of wires appointed pursuant to the provisions of section thirty-two of chapter one hundred and sixty-six. Said notice shall be given by mailing or delivering a permit application form prepared by the board, to said inspector. Any person failing to give such notice shall be punished by a fine not exceeding five hundred dollars. This section shall be enforced by the inspector of wires within his jurisdiction and the state examiners of electricians.
 

electricmanscott

Senior Member
Location
Boston, MA
If I can find a sparky willing to pull the permit and do a final look-over for a reasonable fee (while allowing me to do the labor), I may consider that.



IMO this job is over your head.

More importantly, if you do find an electrician dumb enough to do that for you, and the dummies are out there, do NOT mention it here.

I will drop a dime. That you can count on.
 
IMO this job is over your head.

More importantly, if you do find an electrician dumb enough to do that for you, and the dummies are out there, do NOT mention it here.

I will drop a dime. That you can count on.

The SE portion of the job job is over my head. About 8 feet or so by my measurements.

You're more than entitled to your opinion, but this is a debate I'm looking to avoid. As I said, at this point, I'm merely looking to plan and understand some aspects of it.
 
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