Will 480V three phase generally have a neutral?

Jraef said:
Somebody is probably misinterpreting something here. There is no “3 legs of 277V”. That is a 480V system and for some reason, they are using 3 separate power supplies with each one connected phase to neutral. That might be inside of the unit, but that’s not the same as a 3 phase power supply.

Be that as it may, you cannot be guaranteed that a 480V system in this country will be 480Y277. MOST new systems will be, simply because utilities like simplicity and consistency from a maintenance and spare parts standpoint. But anyone can ask for an exception to have a 480V delta source and get the exception granted if they have sufficient cause. In addition, it USED TO BE quite common for heavy industry. 480V delta was/is used when the cost of an inadvertent shutdown due to a minor ground fault would cause far more economic chaos than that of the lost equipment. So in an ungrounded delta system, the first ground fault simply changes it to a corner grounded delta, and the rest of the plant keeps on chugging along unaware. This concept was VERY common in plants built during WWII, especially if it involved “strategic materials” such as steel, aluminum, mining, textiles, petroleum products and chemicals. The practice continued for a long time afterward and still happens today, just not as often.

I cut my teeth in this industry as an electrician at a steel mill, we were 480V delta. We had “phase lights” in the electric shop and if one of them glowed brighter than the others, that told us there was a ground fault somewhere on that phase. We didn’t know where, so we would all jump into golf carts and spread out across the campus looking for either a column of smoke, or a production manager running around pulling his hair out because his line was down and he wasn’t going to make quota!

In addition, a LOT of sites that only use 480V machinery will have a 4 wire TRANSFORMER from the utility, because that’s the default, and the XO terminal is bonded at the transformer or the service panel. But they don’t bother running a neutral conductor out past that point because the are not using it. This is VERY common in Motor Control Centers, because motors never need the neutral. So if your equipment ends up at a place like that, it’s not going to work. Someone needs to rethink this design IMHO…
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A lot of Water and sewage plants do that.
 
I went to the datasheet, and there are 3 different connections diagrams.

480V wye, 240V delta, and single phase.

From these diagrams, I think we can infer that there are 3 separate single phase inputs, rated 196-305V, that the N terminals can be up to 120V different from ground, and that the L terminals can be up to 528V apart.

In the 480V wye configuration there is a chance that the neutral is necessary to force balance between the separate inputs.
 
winnie said:
I went to the datasheet, and there are 3 different connections diagrams.

480V wye, 240V delta, and single phase.

From these diagrams, I think we can infer that there are 3 separate single phase inputs, rated 196-305V, that the N terminals can be up to 120V different from ground, and that the L terminals can be up to 528V apart.

In the 480V wye configuration there is a chance that the neutral is necessary to force balance between the separate inputs.
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Yeah, most likely to make it universal without having to make major changes.
 
Jraef said:
Somebody is probably misinterpreting something here. There is no “3 legs of 277V”. That is a 480V system and for some reason, they are using 3 separate power supplies with each one connected phase to neutral. That might be inside of the unit, but that’s not the same as a 3 phase power supply.

Be that as it may, you cannot be guaranteed that a 480V system in this country will be 480Y277. MOST new systems will be, simply because utilities like simplicity and consistency from a maintenance and spare parts standpoint. But anyone can ask for an exception to have a 480V delta source and get the exception granted if they have sufficient cause. In addition, it USED TO BE quite common for heavy industry. 480V delta was/is used when the cost of an inadvertent shutdown due to a minor ground fault would cause far more economic chaos than that of the lost equipment. So in an ungrounded delta system, the first ground fault simply changes it to a corner grounded delta, and the rest of the plant keeps on chugging along unaware. This concept was VERY common in plants built during WWII, especially if it involved “strategic materials” such as steel, aluminum, mining, textiles, petroleum products and chemicals. The practice continued for a long time afterward and still happens today, just not as often.

I cut my teeth in this industry as an electrician at a steel mill, we were 480V delta. We had “phase lights” in the electric shop and if one of them glowed brighter than the others, that told us there was a ground fault somewhere on that phase. We didn’t know where, so we would all jump into golf carts and spread out across the campus looking for either a column of smoke, or a production manager running around pulling his hair out because his line was down and he wasn’t going to make quota!

In addition, a LOT of sites that only use 480V machinery will have a 4 wire TRANSFORMER from the utility, because that’s the default, and the XO terminal is bonded at the transformer or the service panel. But they don’t bother running a neutral conductor out past that point because the are not using it. This is VERY common in Motor Control Centers, because motors never need the neutral. So if your equipment ends up at a place like that, it’s not going to work. Someone needs to rethink this design IMHO…
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Excellent point.
We do not supply a true delta service. We bring the neutral to the CT cabinet, or Meterbase, or stack, depending on delivery point.
It’s up to the electrician whether or not he uses it.
 
I just wanted to chime in here, I was just working at a site today, 480 volts, the neutral does not extend beyond the service equipment, there are no neutrals anywhere.

I would suggest to the OP, use a 480:120 transformer to power your power supply, or something like that. They are readily available and everybody understands them.
 
Birken Vogt said:
I just wanted to chime in here, I was just working at a site today, 480 volts, the neutral does not extend beyond the service equipment, there are no neutrals anywhere.

I would suggest to the OP, use a 480:120 transformer to power your power supply, or something like that. They are readily available and everybody understands them.
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From the wiring sheet the op provided, the loads are single phase, 305 volts or less, so no 480 loads, that is why they want the 277 volts, it’s not just the controls needing the neutral, all loads need the neutral. If a neutral is not available, they would need a 480 delta to 480 wye four wire transformer if an existing feed is used, unless a new circuit or feeder is installed from where the neutral is present.
 
Thinking on this: we have a strong guess that the power supply is 3 separate switching rectifiers operating with their outputs in parallel, and sharing the DC load.

If everything is perfectly balanced, this should also be a balanced load on the 480V side, and virtually no current should flow on the neutral.

But these are three constant power loads, if the input voltage drops, the input current rises. This means that the input impedance changes as the square of the applied voltage.

Without the neutral reference present, the system is in unstable equilibrium. Say a random fluctuation drops the voltage to one leg: that leg will try to draw more current, and its voltage will drop further. Pretty quickly one of the internal power supplies is operating near its minimum voltage and the other two are in an over voltage state.

But with the neutral present, everything stays close to balance and little current flows on the neutral.

Speculation: the neutral reference could be supplied by a small zig-zag transformer in the machine, with a pure 3 wire supply external to the machine.

This would address installations where the service is grounded wye but the neutral is not brought into the plant. It might also work with corner grounded or ungrounded systems, but that would require additional evaluation of the insulation system between the circuit and ground.
 
fastline said:
Not saying I've seen it all, but in my industrial years, I've never seen a 277V specific device other than 1P lighting. Never 3 phases of 277.
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277 volt quartz tube heaters were once pretty common thing. I think there is other heater units from radiant heaters to unit heaters commonly available in 277 volts. May not be stocked in many places but manufacturers do have catalog numbers for them. I've seen 277 volt rated water heaters as well. In fact I connected one about a year ago in a new home, to 240 volts. Not my idea and not sure how well it is working out for the owner. Plumber's idea, it was a unit that would heat both upper and lower element simultaneously, it was his idea to use this instead of two separate units. Don't remember the rating anymore but after calculating for difference when connected to only 240 volts I remember I ran a 50 amp circuit to it.
 
hillbilly1 said:
From the wiring sheet the op provided, the loads are single phase, 305 volts or less, so no 480 loads, that is why they want the 277 volts, it’s not just the controls needing the neutral, all loads need the neutral. If a neutral is not available, they would need a 480 delta to 480 wye four wire transformer if an existing feed is used, unless a new circuit or feeder is installed from where the neutral is present.
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Quick question-
If a neutral is at the service equipment (that’s where we drop ours off), would it be cheaper to install the transformer or pull in a neutral from the service equipment?
I understand distance of pull, but in general.
I have no idea of the cost of the transformer plus installation.
 
kwired said:
277 volt quartz tube heaters were once pretty common thing. I think there is other heater units from radiant heaters to unit heaters commonly available in 277 volts. May not be stocked in many places but manufacturers do have catalog numbers for them. I've seen 277 volt rated water heaters as well. In fact I connected one about a year ago in a new home, to 240 volts. Not my idea and not sure how well it is working out for the owner. Plumber's idea, it was a unit that would heat both upper and lower element simultaneously, it was his idea to use this instead of two separate units. Don't remember the rating anymore but after calculating for difference when connected to only 240 volts I remember I ran a 50 amp circuit to it.
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I did one at a golf course club house canopy, three phase to a controller with individual 277 volt radiant heaters, six of them.
 
Hv&Lv said:
Quick question-
If a neutral is at the service equipment (that’s where we drop ours off), would it be cheaper to install the transformer or pull in a neutral from the service equipment?
I understand distance of pull, but in general.
I have no idea of the cost of the transformer plus installation.
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From what I gather, it’s around a 20 amp circuit, so it’s a toss up, depending on where the panel is, will a neutral bar need to be installed? Is the panel next to, or in the service equipment, or remote, and neutral would need to be pulled in existing conduit?
 
The OP is proposing a piece of equipment that might go into a number of different facilities. So this is more of a survey about how common 480V (no neutral present) is vs 480/277V, not selecting a transformer vs running a neutral for a specific facility.
 
Hv&Lv said:
Quick question-
If a neutral is at the service equipment (that’s where we drop ours off), would it be cheaper to install the transformer or pull in a neutral from the service equipment?
I understand distance of pull, but in general.
I have no idea of the cost of the transformer plus installation.
Click to expand...
How hard is to pull a neutral into an existing conduit(s), especially if they were not sized for it? 20A probably okay, 200A maybe iffy, 2000A not likely.

For small circuits off of large feeder, like an MCC, my experience has been small transformers are used.
 
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