3phase to single phase

GerryB

Senior Member
How would you compare 3Phase to single phase? What I'm asking is I had a call from a potential customer to look at some work for him. When I got there he showed me his service. I have heard of 3phase residential but never seen it. It is underground 3Phase delta, goes into a trough in the gararge. From the trough there is a nipple up to a 60amp 3phase combination meter and fuses enclosure. (3 60 amp fuses). From there conduit to a panel in the house. Also out of the trough a nipple up to a single phase meter, then a 100 amp breaker and conduit to another panel in the house. (next to the other one). What the HO wants is 200 amps, either combined in one or upping the 60a to 100. The problems, the POCO here will not let you keep the meter in the garage(or basement or wherever) if you are changing anything. Also being underground I would need them to disconnect and reconnect and the engineer said it wouldn't be the same day (We cut and reconnect ourselves on overhead services.) Anyway my question. I was thinking after looking at it that even though one panel is 60amp it is 3 phase and has that extra leg (although you need to be careful with the high leg) Would you say the 60 amp 3phase is almost equivalent to the 100 amp single phase? He wants to add some 240 lines for his daughter to move in, ie: range,. dryer and other kitchen items.
 

Canton

Senior Member
How would you compare 3Phase to single phase? What I'm asking is I had a call from a potential customer to look at some work for him. When I got there he showed me his service. I have heard of 3phase residential but never seen it. It is underground 3Phase delta, goes into a trough in the gararge. From the trough there is a nipple up to a 60amp 3phase combination meter and fuses enclosure. (3 60 amp fuses). From there conduit to a panel in the house. Also out of the trough a nipple up to a single phase meter, then a 100 amp breaker and conduit to another panel in the house. (next to the other one). What the HO wants is 200 amps, either combined in one or upping the 60a to 100. The problems, the POCO here will not let you keep the meter in the garage(or basement or wherever) if you are changing anything. Also being underground I would need them to disconnect and reconnect and the engineer said it wouldn't be the same day (We cut and reconnect ourselves on overhead services.) Anyway my question. I was thinking after looking at it that even though one panel is 60amp it is 3 phase and has that extra leg (although you need to be careful with the high leg) Would you say the 60 amp 3phase is almost equivalent to the 100 amp single phase? He wants to add some 240 lines for his daughter to move in, ie: range,. dryer and other kitchen items.
If I'm understanding what you are saying and asking is that you have a 3-phase center tapped delta to a residential house (240 volt). One is a three phase 60 amp metered service going in the home and another single phase 100 amp metered service going into the home....off the same "underground" service lateral.......? Meters are in the garage....along with service disconnects....? (How would fire department kill power?) Anyway....if you are trying to compare the 3-phase service to the single phase service your KVA is roughly the same available on both...25KVA available.

I'm not really sure what you are asking....?
 

Smart $

Esteemed Member
Location
Ohio
60A 3? is roughly equivalent to 100A 1? in kVA. However, the problem with residential is very little load can be connected to the high leg. Most your residential 240V loads are actually 120/240V. You can however connect some common items to the high leg: large window-type AC (240V only, not 120/240V), water heater, and baseboard heater(s) are the only ones that come to mind. Breakers supplying such loads will have to be straight-rated 240V (not slash-rated 120/240).

First step is to do a load itemization and calculation before proceeding...
 

GerryB

Senior Member
Thanks for the replies. I guess I was asking can you get more load out of a 3? panel then a 1? of the same amperage. Now I don't know about the breakers. If you installed a 120/240v breaker and l leg was 120v and the other 208v would that damage a dryer or a range? I have to admit I didn't know about straight 240v breakers.:dunce:
 

GerryB

Senior Member
Thanks for the replies. I guess I was asking can you get more load out of a 3? panel then a 1? of the same amperage. Now I don't know about the breakers. If you installed a 120/240v breaker and l leg was 120v and the other 208v would that damage a dryer or a range? I have to admit I didn't know about straight 240v breakers.:dunce:
I think I can answer my own question. The breaker itself is not rated for the higher voltage so it will fail?
 

Smart $

Esteemed Member
Location
Ohio
Thanks for the replies. I guess I was asking can you get more load out of a 3? panel then a 1? of the same amperage. Now I don't know about the breakers. If you installed a 120/240v breaker and l leg was 120v and the other 208v would that damage a dryer or a range?...
Depends on whether the appliance or load uses line-to-neutral voltage from the high leg... but I wouldn't risk it. If you decide to go 3?, only use straight 240 breakers on the high leg and power only straight 240V loads. Under this scenario, yes you can get more out of a 3? panel than a 1? with the same rating... but what straight 240V loads there are will limit just how much.
 

Smart $

Esteemed Member
Location
Ohio
...The breaker itself is not rated for the higher voltage so it will fail?
I've not witnessed any 120/240 breakers connected to the high leg, let alone one that 'failed'... so I can't say what will happen... but I can tell you it is a violation. :D
 

GerryB

Senior Member
I've not witnessed any 120/240 breakers connected to the high leg, let alone one that 'failed'... so I can't say what will happen... but I can tell you it is a violation. :D
A little follow up. I called my supply house that handles GE. The counter guy had to check with the techs in back. It is a non stock item. A 2 pole 20a 240volt rated snap in breaker would be $65.00 and not available for 4-6 weeks. My other supply house that handles Seimens also non stock but they haven't called back yet. Finally I checked my garage thinking about 3 pole breakers and found a GE no markings and a sq D that was rated 240volt.
I am thinking the GE 3 pole is 120/240 since I bought one a few months back and it was only about $65. So now I know and can plan ahead.:)
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Meters are in the garage....along with service disconnects....? (How would fire department kill power?)
Does your area require exterior disconnects for all services?

Roger
 

GerryB

Senior Member
Does your area require exterior disconnects for all services?

Roger
They do not require exterior disconnects anywhere in the state (CT) for residential as far as I know if your disconnect (or panel) is located right inside, basement, garage in this instance, only a few feet from the meter. Of course if it is further than that you need the disco outside at the meter. The POCO requires you in most instances to relocate the meters outside if they are inside and you are upgrading. So to answer Canton's question the fire dept would have to wait for the POCO to cut at the pole or smash the door in and turn it off.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
They do not require exterior disconnects anywhere in the state (CT) for residential as far as I know if your disconnect (or panel) is located right inside, basement, garage in this instance, only a few feet from the meter. Of course if it is further than that you need the disco outside at the meter. The POCO requires you in most instances to relocate the meters outside if they are inside and you are upgrading. So to answer Canton's question the fire dept would have to wait for the POCO to cut at the pole or smash the door in and turn it off.
As far as the NEC is concerned, if the raceways were under the slab they could extend to anywhere in the building without exterior disconnecting means, they would be outside the building until they penetrated through the slab and the Service Disconnect(s) could be located there, see 230.6.

Many commercial buildings such as malls for instance have electrical closets behind locked doors well within the building where meter banks and disconnects are located.


Roger
 

GerryB

Senior Member
As far as the NEC is concerned, if the raceways were under the slab they could extend to anywhere in the building without exterior disconnecting means, they would be outside the building until they penetrated through the slab and the Service Disconnect(s) could be located there, see 230.6.

Many commercial buildings such as malls for instance have electrical closets behind locked doors well within the building where meter banks and disconnects are located.


Roger
Right, forgot about that. Also if you run from the meter outside the house a distance and then enter to the panel you are ok too.
 

GerryB

Senior Member
Why are you not Providing a load calc and new service ? Maybe it is time .

I am going to do a load calc to see if he is ok the way it is. In the 60a 3 phase panel he has a 30a 3/phase AC and single phase 30a dryer and 50a hot tub. In the single phase 100a there is one space left and the large loads are a 50a double oven, 40 amp cooktop, well pump and everything else. It is a large ranch house. He says the cooktop with all the burners on is to much to put on the 60a panel with the other items. He wants to add a laundry (another washer and dryer) and a kitchen with a range. So I don't know if things could be swapped around or balanced better but if the 60 amp 3 phase panel was 100 amps he would be ok. The problem is the POCO is not working with him. The engineer told me he should wait till the spring because he would be without power for two days, do a new underground or pull out the old wire and install new. He also called the HO and told him the same. I don't believe there is anything wrong with the old conduit or the wire in it which looks like it is at least 3/0 copper. Also he needs to keep the 3 phase because of the AC. To me the easiest thing to do would be to re feed the 3 phase meter base with #4 thhn (it is now #6), add a 3 phase 100a fused disco, and re feed his 3 phase panel (located in another part of the house along with the 100a) The POCO told him he was on a residential rate so I believe the #4 should be acceptable. I don't want to do it hot or without the POCO approval, so that is my dilemma. It is a very unusual set up I've never come across before.
 

donaldelectrician

Senior Member
Why are you not Providing a load calc and new service ? Maybe it is time .

I am going to do a load calc to see if he is ok the way it is. In the 60a 3 phase panel he has a 30a 3/phase AC and single phase 30a dryer and 50a hot tub. In the single phase 100a there is one space left and the large loads are a 50a double oven, 40 amp cooktop, well pump and everything else. It is a large ranch house. He says the cooktop with all the burners on is to much to put on the 60a panel with the other items. He wants to add a laundry (another washer and dryer) and a kitchen with a range. So I don't know if things could be swapped around or balanced better but if the 60 amp 3 phase panel was 100 amps he would be ok. The problem is the POCO is not working with him. The engineer told me he should wait till the spring because he would be without power for two days, do a new underground or pull out the old wire and install new. He also called the HO and told him the same. I don't believe there is anything wrong with the old conduit or the wire in it which looks like it is at least 3/0 copper. Also he needs to keep the 3 phase because of the AC. To me the easiest thing to do would be to re feed the 3 phase meter base with #4 thhn (it is now #6), add a 3 phase 100a fused disco, and re feed his 3 phase panel (located in another part of the house along with the 100a) The POCO told him he was on a residential rate so I believe the #4 should be acceptable. I don't want to do it hot or without the POCO approval, so that is my dilemma. It is a very unusual set up I've never come across before.

WOW !

How old is the 3ph ac compressor . New 1ph compressor with new service maybe ?




Don
 

GerryB

Senior Member
WOW !

How old is the 3ph ac compressor . New 1ph compressor with new service maybe ?

The ac came with the house. I didn't ask him how long he was there. I noticed something else I didn't mention in the post before. The 3phase panel is right next to the single phase panel, both about 70 feet into the house. They ran the 3 legs from the fuses in rigid conduit, no neutral. There is a nipple between the two panels and they stole a neutral from the 100a panel, a 1/2 offset nipple with a white #6 in it:eek:. Yeah, he needs some work. If the compressor is 20 years old or so that would be a good idea anyway. Some one can make a mistake with that high leg also. Another thing a previous post by Smart$ talked about 240volt rated breakers as opposed to 120/240volt. This is a SqD panel, (not homeline). The 3pole ac breaker says 240v on it. The 2pole breakers are 120/240volt. I haven't talked to sqD yet but I know one of those breakers is on the high leg, so that might not be right either. This guy lives close by so I kind of don't mind going over there, I'm learning something:roll:


Don
 

Smart $

Esteemed Member
Location
Ohio
This is a SqD panel, (not homeline). The 3pole ac breaker says 240v on it. The 2pole breakers are 120/240volt. I haven't talked to sqD yet but I know one of those breakers is on the high leg, so that might not be right either.

You can use 120/240 breakers in a 240/120V 3? 4W panel, but no pole can be on the high leg.
 
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