The owner of a 100 year old apartment building with 22 small (600 sq ft each) suites is in the process of upgrading the electricals, plumbing, and other areas. There will be no major electric appliances, no laundry, and nothing requiring 240 VAC in any apartment. Central steam heat and hot water systems are natural gas. Looks like the load for general lighting and small appliance circuits for each apartment will be 20 amps at 120 VAC. Is it feasible to use 60 amp single phase panels in each apartment with the two line buses connected together, which would only provide 120 VAC but would only require 3 wires to feed? It would be advantageous to use a 208Y/120 service for the building rather than 120/240. Does anybody have experience with this?
Use 120 ONLY to feed apartments
- Thread starter sgunsel
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zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
If you connect the two line busses together, you can easily overload the neutral bus.
- Location
- Massachusetts
Not really.
- Location
- Massachusetts
Yeah, we install a 3 phase main with modular single phase meters.
- Position 1 connects to A&B
- Position 2 connects to A&C
- Position 3 connects to B&C
This repeats as many times as needed.
I would bring 208/120 to each unit.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Bob, should that be 120/208 for single phase? Connected off a three phase source.
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- Location
- Massachusetts
Maybe, ....... give me a break. I had a 3 hour service call with 6 hours of driving last night, it was a 325 mile round trip.
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Maybe, ....... give me a break. I had a 3 hour service call last night at 11PM and it was a 325 mile round trip.
Okay, I be nice-but just this once.
- Location
- Massachusetts
After doing a very simple load calculation based upon the square footage given and several assumptions (no AC, no fastened in place microwave, no laundry, no garbage disposal, no dishwasher and also assumed a gas fired range) I came up with approximately 30 amps for each apartment.
It wouldn't take a lot to go beyond the 60 amps that is proposd if some of the loads I left out were introduced.
Short of that, an NEC related reason to not do as you have proposed escapes me.
Pete
It wouldn't take a lot to go beyond the 60 amps that is proposd if some of the loads I left out were introduced.
Short of that, an NEC related reason to not do as you have proposed escapes me.
Pete
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- Location
- Massachusetts
I think with a 22 unit building we are looking at AC or MC feeders at a minimum.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Not to mention that it probably goes against the product listing.
From a major manufacturer's FAQs- Answer: XXX does not offer a 120V load center above 2 spaces.
M4gery
Senior Member
Hmmmm, you're probably right.
There are a lot of older condo/apartment buildings in my area around that size that are stick built and romex filled, so you never know.
kbsparky
Senior Member
- Location
- Delmarva, USA
I'd be willing to bet that the OP has a project in which there is no egc present in the feeder cables. By using the existing 3-wire feeder as a hot, neutral, and ground, only 120 Volts would be available for branch circuits in each unit.
Jumpering the buss bars together in the subpanels could be an acceptable alternative, as long as the connected 120 Volt loads do not exceed the feeder cable's rating.
Jumpering the buss bars together in the subpanels could be an acceptable alternative, as long as the connected 120 Volt loads do not exceed the feeder cable's rating.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Or the bus bar's (panel's) rating. IMHO, it's really not good practice. The 40a 120/208v solution is great, if you have four conductors.
kwired
Electron manager
- Location
- NE Nebraska
Is there separate meters for each unit? If not overcurrent devices do not need to be in the units but the tenants do need to have access to them unless the place has on site staff that can be reached for incidents where access would be needed. Description of spaces sounds like a hotel - probably once was a hotel.
There will be separate meters for each unit, located in the basement of the building. No idea what original occupancy was, probably apartments, as it is now. Even a window AC would add less than 15 amps, and at worst case, breakers would limit total current. This will be subsidized housing, small apartments, and with only 120 VAC available. Why would 60 amps not be sufficient for such units? There is a limit to how many toasters and coffee makers can be expected, and there is protection against overdoing those. I can't see how more than 60 amps is likely. They have been at 20 amps per apartment for at least the last 25 years, if not 100.
M4gery
Senior Member
Here's my opinion, you said twice how there will be breakers to limit the current and prevent overloading, but do you really want to depend on that in a new electrical installation? Why not install what they need so that you don't have to expect overloading?
Yes, there is a limit to how many toasters and coffee makers the average person uses, but what is the limit? Would it be that odd for a coffee maker, toaster, microwave, and television all to be running while making breakfast in the morning while someone is in the bathroom using a hairdryer? Now what if 2 window AC units are running during this, what would that load look like?
Isn't that why they are upgrading??
kwired
Electron manager
- Location
- NE Nebraska
Something else to consider is voltage drop and conductor size of the feeders.
Your proposed 60 amp 120 volt feeder will power the same VA as a 30 amp 120/240 feeder but will have more voltage drop to consider. 2 #6 and 1#10 cost more than 4 #10 and require larger raceway to contain. How do you plan to jump the panel busses together? You can't put two conductors in the lugs so you will need to purchase some kind of connector. Polaris connectors are easy but not low enough cost to make it obviously less when all is done.
If your intent was reduced installation cost then examine it again. It may not be less. You also mentioned using three phase 120/208. It looked to me like the total load was able to be supplied from 200 amp single phase - adding three phase distribution will be more expensive. Three phase is a good idea if the load is there to justify it.
Your proposed 60 amp 120 volt feeder will power the same VA as a 30 amp 120/240 feeder but will have more voltage drop to consider. 2 #6 and 1#10 cost more than 4 #10 and require larger raceway to contain. How do you plan to jump the panel busses together? You can't put two conductors in the lugs so you will need to purchase some kind of connector. Polaris connectors are easy but not low enough cost to make it obviously less when all is done.
If your intent was reduced installation cost then examine it again. It may not be less. You also mentioned using three phase 120/208. It looked to me like the total load was able to be supplied from 200 amp single phase - adding three phase distribution will be more expensive. Three phase is a good idea if the load is there to justify it.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
A cheap solution to getting 120v to both phases would be a 2-pole backfed breaker with a conductor between the poles of the breaker.
I would stick with 120/208 without a great reason for getting weird. If this were a solar installation you'd be required to put a warning on any straight 120v panel warning against multiwire circuits. While not required for a non-solar installation, it seems prudent.
I've wired 42-plexes in NM, you need to ascertain the construction type to know if you can use NM or not.
I'd imagine when all is said and done, 8/3 AL SER cable is going to be the cheapest way to go with the most bang for your buck.
I would stick with 120/208 without a great reason for getting weird. If this were a solar installation you'd be required to put a warning on any straight 120v panel warning against multiwire circuits. While not required for a non-solar installation, it seems prudent.
I've wired 42-plexes in NM, you need to ascertain the construction type to know if you can use NM or not.
I'd imagine when all is said and done, 8/3 AL SER cable is going to be the cheapest way to go with the most bang for your buck.
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