# Multi family service question



## yankeejoe1141 (Jul 26, 2013)

Hello guys, this week I went to look at a multifamily building for a service upgrade. The house has three units and currently 2 meters. The first floor has it’s own meter, and the owner lives on the second floor and pays for the other meter that does her second floor unit and the small third floor unit also. She wants to add a meter so if she sells it she can sell it as a legal three family. I told her we really need to add two meters, an additional one for the common areas like the laundry in the basement. 

So I think if I get a four socket meter enclosure and install one - 100 amp breaker for the first floor, one - 100 amp breaker for the second floor, one - 60 amp breaker for the third floor, and one - 60 amp breaker for the basement and common areas, this will bring me up to a 320 amp service all together.

So I guess what I’m asking is how do I size the wire from the meter enclosure to the overhead point of attachment? I figured I need to size it for 320 amps, but I happen to run into someone from the poco this week and asked him and he said he would just leave it at a 200 amp service feeding all four meters. I don’t think it sounds right to me but it would be so much easier to run 4/0 alum to the thing instead of larger wire and conduit. 

I’m looking for other opinions because I think there would be nothing to stop potentially 250 amps from being loaded on a 200 amp service if I did it his way, but he insisted he sees this set up all the time.

Thanks


----------



## Kevin (Feb 14, 2017)

Not sure how it works in your area, but here I have put several 3 and 4 gang meterbases on a 200 amp riser. Apartments usually get only 60 amps, although existing is existing, so I'd be tempted to leave it.

Where I am we don't just add up the amperage of all the services. Doing that _is_ possible, but it just means you're more likely to never use the maximum amperage... what are the chances that 3 apartments are going to be using tons of current at the same time?

Anyway, I'm not in the same country as you, so I cannot comment more.


----------



## Dark Knight (Jan 6, 2016)

Take the meter numbers to POCO and ask for usage history. Nothing is changing, it’s still 3 tenants and shared common area. If 200 was fine before it’ll be fine now. Usage is probably barely higher than if it was a single occupancy. Canadian as well, but that’s what I would do here in this situation.


----------



## Cow (Jan 16, 2008)

Since you don't have a single main, the service conductors only have to be sized to carry the calculated load.

The simplest is to do as Dark Knight mentioned and get the peak demand history for the last 12 mos from your utility, then it's as easy as showing the inspector the report at inspection time.


----------



## yankeejoe1141 (Jul 26, 2013)

Thanks guys, I‘d love just to use a 200 amp meter riser, that’s why I’m trying to justify it to myself. I was only thinking the first two floors should get 100 amp mains because each has an electric range so I did a quick load calculation and came out with that. I don’t think I could give them 60 amp mains with the ranges there. I agree that I shouldn’t just add up the main breakers and that’s the size of the service since we‘re really not adding anything new, but if I don’t do that then what protects the riser from overload? I would feel like I’m leaving up to chance. Our code book says we can use an 83% demand factor on the service to a single family residence, or to the feed to individual units in a multi family dwelling. But I don’t see any language that I could apply a demand factor to a service for multi-family.


----------



## yankeejoe1141 (Jul 26, 2013)

Cow said:


> Since you don't have a single main, the service conductors only have to be sized to carry the calculated load.
> 
> The simplest is to do as Dark Knight mentioned and get the peak demand history for the last 12 mos from your utility, then it's as easy as showing the inspector the report at inspection time.


So if I go by what my calculated load is, then I need to size the wires to about 220 amps. I’m going to try and get the demand history, but I still feel like I’m not covered if they buy a bunch of stuff after I leave and overload the service.


----------



## Dark Knight (Jan 6, 2016)

You don’t have to worry about it because the code allows it. For good reason. I don’t know how the NEC does it, but I imagine it’s similar to the CEC. You don’t have to add up the 4 meter demands to get your main service size. Here you take your biggest demand at 100 percent, your next 2 biggest at 65 percent, and your next 2, or in your case last one, at 40 percent and add those up. The reason this works is because the chances of 2 suites using the oven at the exact same time for an extended period of time is 50/50? Maybe a little higher? The chances of all 4 suites using the oven at the same time are minuscule. There’s only one dryer so you don’t need to worry about that. Other than that, all other loads are minor and 120 volts. But if it helps you sleep at night, but a 400 amp rated, 4 position meter base in as opposed to a 200 amp rated one (the price difference is about 500% more on the 400 amp) and run your 200 amp risers. If there’s a problem in the future, all you need to do is upgrade your riser.


----------



## HertzHound (Jan 22, 2019)

Your sheet is for the feeders to each apartment. You would do it a little different for the service entrance conductors.

In you sheet you you are doing the first 3,000VA over and over. That is giving you a higher number if you are adding up the units in the end. So the first 3,000 for all units, then the rest of all units at 35% will give you a lower number.

The two ranges should be a total of 11KW on the service. You are adding them together and getting 16KW


----------



## yankeejoe1141 (Jul 26, 2013)

HertzHound said:


> Your sheet is for the feeders to each apartment. You would do it a little different for the service entrance conductors.
> 
> In you sheet you you are doing the first 3,000VA over and over. That is giving you a higher number if you are adding up the units in the end. So the first 3,000 for all units, then the rest of all units at 35% will give you a lower number.
> 
> The two ranges should be a total of 11KW on the service. You are adding them together and getting 16KW


Thanks, that actually makes sense to me and makes me feel a little better about using 4/0 alum service conductors.

I guess I’m the only one who feels like I’m leaving a lot to chance by feeding four meters with those conductors and no real protection.

This is my first time with a multi family but it sounds like you guys that have more experience are comfortable with that arrangement. Has anyone ever had a past experience where there was a problem with the riser size?


----------



## yankeejoe1141 (Jul 26, 2013)

HertzHound said:


> Your sheet is for the feeders to each apartment. You would do it a little different for the service entrance conductors.
> 
> In you sheet you you are doing the first 3,000VA over and over. That is giving you a higher number if you are adding up the units in the end. So the first 3,000 for all units, then the rest of all units at 35% will give you a lower number.
> 
> The two ranges should be a total of 11KW on the service. You are adding them together and getting 16KW


HertzHound, what app is that you took that screen shot from?


----------



## Dennis Alwon (May 9, 2009)

You don't need to add the mains to size the riser. If you know how to do a service calc then you can get by with that as the riser size


----------



## HertzHound (Jan 22, 2019)

yankeejoe1141 said:


> HertzHound, what app is that you took that screen shot from?


It’s the 2017 NEC ePub. I guess I could use another e-reader app, but when I downloaded the ePub from NFPA it installed their e-reader. Unfortunately they decided to not sell an ePub or PDF for 2020. Now it looks like the only way to get an electronic version is with a $9.00 a month subscription. I just ordered a 2020 NEC book this weekend because my update classes start December 5. This will be my first actual book in two code cycles.

In the screenshot it says page 76 of 314. So there must be 314 pages just in that section, not the whole book.


----------



## HertzHound (Jan 22, 2019)

And you are correct. You cannot reduce the service entrance conductors by 83% like you can for a single family dwelling.


----------



## yankeejoe1141 (Jul 26, 2013)

HertzHound said:


> It’s the 2017 NEC ePub. I guess I could use another e-reader app, but when I downloaded the ePub from NFPA it installed their e-reader. Unfortunately they decided to not sell an ePub or PDF for 2020. Now it looks like the only way to get an electronic version is with a $9.00 a month subscription. I just ordered a 2020 NEC book this weekend because my update classes start December 5. This will be my first actual book in two code cycles.
> 
> In the screenshot it says page 76 of 314. So there must be 314 pages just in that section, not the whole book.


Oh that’s funny because that‘s what threw me off, I was wondering what app had only 314 pages and was that useful. It’s too bad they don’t offer the same for the 2020 because it looks helpful!, but I won’t sign up for a subscription service.


----------



## yankeejoe1141 (Jul 26, 2013)

HertzHound said:


> And you are correct. You cannot reduce the service entrance conductors by 83% like you can for a single family dwelling.


Thanks - this may be the heart of my confusion. I feel like I’m only reading code for single family and individual units of a multi family but I don’t feel like I’m reading anything that is relevant to the service of a multi family.


----------

