Some of the northern states near the Great Lakes, I'm told. (Been corrected on it before). Also on ships.
3 Phase Service Question
- Thread starter Doubled33
- Start date
Some of the northern states near the Great Lakes, I'm told. (Been corrected on it before). Also on ships.
Snapped-off
Well-known member
415/240 is becoming common in datacenters in the US.
You can fill out a sub panel with more breakers with this distribution setup. It's all about density.
wyliesdiesels
Well-known member
using 277v rated single poles for 240v rated servers?
plenty of good motors rated for 208. anything with a W22 or a hitachi motor on it often has the rating.
or you can program your VFD for AVR and let it magic it out.
service where I work is 240V 1600A corner delta service. tapped hot, too.
wyliesdiesels
Well-known member
oh boy. corner-grounded delta is a special kind of animal that confuses even experienced sparkies to no end... those are fun to work on too, what with the special provisions for grounding and bonding.... they are getting rarer and rarer as PoCos dont want to deal with them anymore....
Last edited:
And of course the office is 208Y, and there's a separate low voltage transformer & panel for the shop 120V loads. half the machinery is 120V controls (local control transformer).
Assume nothing, test everything!
toplessHO
Well-known member
All the more reason to have permanent,engraved labels, on all equipment
Ive been spoiled all these years by following behind architects that actually require that.
Ive been spoiled all these years by following behind architects that actually require that.
Sadly, an architect couldn't have been further removed from any step of "designing" this place.
Codyboy
Well-known member
I've never heard of 240 delta.
At the poco we had 480 ungrounded delta that utilized 240/480 transformers.
We left it ungrounded (straight 480 to the customer) .
The electrician was allowed to ground a corner if needed/ wanted, usually for a reference point.
Yes on special provisions especially if we needed to phase in two separate banks together.
In order to do that we had to establish a ground on one of the phases.
You'd better be dang sure there was no existing ground and if there was you had to know which phase it was.
Yeah the poco's use 277 transformers now when they need to replace a bank. Most all 240/480 transformers are hard to come by except for freeway lighting.
wyliesdiesels
Well-known member
this is surprising.
120/240 3Ø Delta is pretty common where majority of customer loads are single phase and customer just has a few 3Ø loads...
Codyboy
Well-known member
No , I know about 120/240 delta (closed or open) But that is not 240 "corner grounded" delta ,but is grounded (center tapped) to give the customer 120.
If a corner grounded 240 delta existed (and it may somewhere) the customer would not get any 120. In fact they would get 5 readings of 240 volts.
wyliesdiesels
Well-known member
we have several corner grounded 240 Delta services here in town. they do exit... but not very common anymore
I don't get what the big fuss is about, personally. I don't see it as much different from an appliance on a 10-30 cord, except it's all in metal pipe.
Once you're not at 120V to ground anymore, they're all (extra) dangerous. at this point i think the rarity is the main issue. it's not caused me a single problem.
it's fun watching someone realize that wiring a 3 phase load is almost the same as wiring a single phase load out of the same panel though.
wyliesdiesels
Well-known member
except a nema 10-30 has no ground terminal
yes rarity and ignorance about it are the issues not the system itself.
Codyboy
Well-known member
I don't have enough fingers and toes to count the times I've gone on a bad voltage call on straight 480 service whether it be delta or wye.
Sewer or water well from the city guys would call it in.
"Well we're not getting 277 only 480"
Well yeah ugh let me splane something and how things work.
Then it was a 20 minute crash course in different systems and how the system they had at this facility has been working for the past 20 years and you are getting correct voltage. Most understood, some I just verified 480 three times and drove away while they're scratching their head.
Brandon_oma#692
Well-known member
Piggybacking on this. Wondering how my place is. 2 transformers. My understanding is 1 makes leg a and leg c 120 to ground and the other is for the b leg for 3 phase only that is 208 to ground. Not the best picture. These are for my property only.
Codyboy
Well-known member
Thats an open delta bank.Piggybacking on this. Wondering how my place is. 2 transformers. My understanding is 1 makes leg a and leg c 120 to ground and the other is for the b leg for 3 phase only that is 208 to ground. Not the best picture. These are for my property only.
N-L1 120V, N-L2 120V, N-HIGH LEG 208V, L1-L2 240V, L1-L3 240V, L2-L3 240V.
that drawing above is pants on head ...very co fusing way to draw that. Gave me a headache.
Codyboy
Well-known member
wyliesdiesels
Well-known member
thats correct. its called an OPEN delta. same voltages as a CLOSED delta (3 cans) but only 58% of the capacity of a CLOSED (or full) delta.... watch out for that stinger/hi-leg....Piggybacking on this. Wondering how my place is. 2 transformers. My understanding is 1 makes leg a and leg c 120 to ground and the other is for the b leg for 3 phase only that is 208 to ground. Not the best picture. These are for my property only.
With a delta secondary you can completely remove 1 transformer and you still get all 3 phases.
Neat thing is with a wye primary you can provide this 3 phase service with only two primary phases and a neutral. We see it fairly often in the country. Sometimes they have single phase service and the utility will extend a different single phase line from the opposite direction and set the second transformer.
Neat thing is with a wye primary you can provide this 3 phase service with only two primary phases and a neutral. We see it fairly often in the country. Sometimes they have single phase service and the utility will extend a different single phase line from the opposite direction and set the second transformer.
Brandon_oma#692
Well-known member
thank you.
Codyboy
Well-known member
Can you expound on the claimed lesser capacity?
Now I can possibly see that if using the same size transformers on open or closed delta that may be true. Due to the fact the ties on the power transformers help with the load on the lighter (center tapped transformer).
On our 12kv system we would almost always build closed deltas. This would utilize all 3 primary phases for balancing the load across the circuit. This was possible to build closed deltas because the primary winding was open (2 bushings pots) and floated(not grounded). Ungrounded wye, grounded delta.
On our 35kv system we could only build open delta because the one end of the primary coil was grounded to the case of the transformer (1 bushing pots) .
In that case due to load requirements by the customer the transformer size increased.
wyliesdiesels
Well-known member
its because you only have 2 cans not 3. so of course the capacity would be less.... youre missing 1 coil
I've never really understood when described that way either.
If you have a closed Delta with 3
(3) 50 KVA cans you have a 150kva transformer bank.
If you have (2) 50kva cans then the derating should start with 100kva. Why would the math start with 150? Makes no sense to me.
Codyboy
Well-known member
I guess that's why we would up the transformer size then when we built open deltas.
But I get what you're saying. Like for like it would be less capacity with an open delta.
But that can be remedied.
Brandon_oma#692
Well-known member
Just got home and looked. 25kva and 10 kva. I am guessing it is what they could find that day. Comed (utility) was actually here before the Sherriff as they were on the way back to the yard from some other job and came to my mess as a surprise. They had to go get everything and I had power a few hours later. Just realized today what the sizes are. They said to call if I ever had a problem and they would swap them. No clue how much power I can pull?
Someone ran off the road and took out the pole a couple years ago. I came home from work to the pole in my driveway and the transformers busted open all over.
Someone ran off the road and took out the pole a couple years ago. I came home from work to the pole in my driveway and the transformers busted open all over.
Codyboy
Well-known member
On a small bank like that a 200A service.
A 25 kva is good for 100 amps per leg was the common in the field assessment.
But you could overload it by 25% .
And yes , a 200 amp service can do 200 amps per leg continuously but that's not the case most times. He'll if it were you probably wouldn't want to pay that bill every month.
A typical house will run around 20 to 40 amps per leg with ACs , fridges, deep freezers, and lights.
My smart meter tells me how much kva I've peaked. 2700 sf and I think it's 16 kva. But I do have a gas furnace. So that helps.
It's normal to have a smaller transformer for the power pot. Usually one size smaller sometimes two sizes as is your case.
And that's due to the 3 phase load is usually not much. AC and maybe a well pump.
A lot of the older areas in town had 3 phase ACs, don't see it that much nowadays.
A 25 kva is good for 100 amps per leg was the common in the field assessment.
But you could overload it by 25% .
And yes , a 200 amp service can do 200 amps per leg continuously but that's not the case most times. He'll if it were you probably wouldn't want to pay that bill every month.
A typical house will run around 20 to 40 amps per leg with ACs , fridges, deep freezers, and lights.
My smart meter tells me how much kva I've peaked. 2700 sf and I think it's 16 kva. But I do have a gas furnace. So that helps.
It's normal to have a smaller transformer for the power pot. Usually one size smaller sometimes two sizes as is your case.
And that's due to the 3 phase load is usually not much. AC and maybe a well pump.
A lot of the older areas in town had 3 phase ACs, don't see it that much nowadays.
micromind
Well-known member
The open ∆ was very common many years ago when a building had a ton of 120 loads and one or two fairly small 3Ø motors, like a boiler fan and feed pump.
Think of it as a single phase service with the high leg added on to get 3Ø.
Some people say that an open ∆ service has unstable voltage......not true. The majority of switchgear operating at 4160 and higher will have potential transformers that reduce the high voltage to 120 or thereabouts for the purpose of voltage monitoring. These transformers have very little load (usually a few miliamps) and are almost always connected open ∆ with the common wire (phase B) grounded. Instruments need accurate voltages and the open ∆ system will provide it.
I've never seen the high leg to neutral but it certainly could be. Circuit breakers that will fit a standard 240 volt panel and are rated 240 to neutral do exist but the short circuit interrupting rating is low. I have seen (and installed) 240 single phase loads the used the nigh leg and one of the other phases. For this, you'll need a 240 volt 2 pole breaker, not a 120/240 model.
I've seen open ∆ systems with a 100KVA transformer for 120 loads and a 10KVA for the high leg.
Think of it as a single phase service with the high leg added on to get 3Ø.
Some people say that an open ∆ service has unstable voltage......not true. The majority of switchgear operating at 4160 and higher will have potential transformers that reduce the high voltage to 120 or thereabouts for the purpose of voltage monitoring. These transformers have very little load (usually a few miliamps) and are almost always connected open ∆ with the common wire (phase B) grounded. Instruments need accurate voltages and the open ∆ system will provide it.
I've never seen the high leg to neutral but it certainly could be. Circuit breakers that will fit a standard 240 volt panel and are rated 240 to neutral do exist but the short circuit interrupting rating is low. I have seen (and installed) 240 single phase loads the used the nigh leg and one of the other phases. For this, you'll need a 240 volt 2 pole breaker, not a 120/240 model.
I've seen open ∆ systems with a 100KVA transformer for 120 loads and a 10KVA for the high leg.
Steve from Socal
Well-known member
On the other end of the open delta transformer saga. I have a 3HP grinder I bought from a guy in up state New York, it was listed as 460 volt. I got it home and cleaned the layers of paint of the data plate, 550 volt machine. It ran on 480 but was down on power, looked for a transformer with no luck. Ended up using two small control transformers open delta.