Will 480V three phase generally have a neutral?

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cowski

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I work for an OEM. We have a new product that requires 460V with a neutral (277V) to run.

If our customers have 480V service will they generally have a neutral tap as well? Or is that a risky assumption?

I know it's common to run 480V three phase without a neutral to individual machines that don't require it... But is there generally a neutral conductor available in the panelboard?

I'm just trying to get a sense... will there be a neutral 90% of the time? Or 50%? Will there typically be a neutral but it might need to be run super far?
 
cowski said:
I'm just trying to get a sense... will there be a neutral 90% of the time? Or 50%? Will there typically be a neutral but it might need to be run super far?
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It more than likely would depend on the type of building. A manufacturing plant may have only 3Ø, 3W, 480 volts. A commercial building if it has 480 will almost always be 3Ø, 4W, 480Y/277.
 
cowski said:
I work for an OEM. We have a new product that requires 460V with a neutral (277V) to run.

If our customers have 480V service will they generally have a neutral tap as well? Or is that a risky assumption?

I know it's common to run 480V three phase without a neutral to individual machines that don't require it... But is there generally a neutral conductor available in the panelboard?

I'm just trying to get a sense... will there be a neutral 90% of the time? Or 50%? Will there typically be a neutral but it might need to be run super far?
Click to expand...
In my industrial work, while the 5kV to 480Y/277 volt transformers had XO bonded, we only ran a supply side bonding jumper and not a neutral from the transformer to the switchgear. You would would pretty much need to add a transformer to get 277.
 
infinity said:
It more than likely would depend on the type of building. A manufacturing plant may have only 3Ø, 3W, 480 volts. A commercial building if it has 480 will almost always be 3Ø, 4W, 480Y/277.
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Mostly agreed... in the plants I used to visit before going into data centers, just about everything on the floor was 3p/3w, but there would typically be lighting panels strategically located with 3p/4w.
 
Thanks! That gives me an idea. Yes I've heard that lighting often uses the same 3Ø, 4W, 480Y/277 that I'm looking for...

For a building with 3Ø, 4W, 480Y/277, is there a separate transformer to get 240 single phase? Or wold the transformer have additional taps for single phase 240V?

I'm assuming all buildings with 480 will have 240 single phase as well. If it's a high leg delta with no center tap then I won't get my 277...

Just curious where the 240V comes from if power into the building is 3Ø, 4W, 480Y/277...
 

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I would not design equipment that requires 277 V, especially in an industrial environment. We stopped running neutrals on 480V systems 20 years ago. If 277 V lighting was desired, we installed a small 480 - 480/277 V transformer to supply only lighting loads. For commercial buildings, most will still have neutrals running everywhere - probably more than 50% but less than 90% But keep in mind that many commercial building have only 208/120 V available.
 
cowski said:
Thanks! That gives me an idea. Yes I've heard that lighting often uses the same 3Ø, 4W, 480Y/277 that I'm looking for...

For a building with 3Ø, 4W, 480Y/277, is there a separate transformer to get 240 single phase? Or wold the transformer have additional taps for single phase 240V?

I'm assuming all buildings with 480 will have 240 single phase as well. If it's a high leg delta with no center tap then I won't get my 277...

Just curious where the 240V comes from if power into the building is 3Ø, 4W, 480Y/277...
Click to expand...
Unlikely. The lower voltage system will most likely be 208Y/120 and not 240. There are some rare cases where there would be a four wire high leg 240 volt delta system with 240 line to line, 120 to the neutral on two phase, and the high leg, 208 to neutral on the 3rd phase.
 
cowski said:
Thanks! That gives me an idea. Yes I've heard that lighting often uses the same 3Ø, 4W, 480Y/277 that I'm looking for...

For a building with 3Ø, 4W, 480Y/277, is there a separate transformer to get 240 single phase? Or wold the transformer have additional taps for single phase 240V?

I'm assuming all buildings with 480 will have 240 single phase as well. If it's a high leg delta with no center tap then I won't get my 277...

Just curious where the 240V comes from if power into the building is 3Ø, 4W, 480Y/277...
Click to expand...
What kind of load are we talking about? 30 amps or less? If this is a large piece of equipment, say 100 amps or more, and the 277 volt load is only 10 amps or so, then you will have a pissed off electrician pulling a full size neutral. If it’s a split up 277 volt load, which I have seen for heating, then a neutral would be acceptable. I hooked up a glass tempering oven last year, that required a 600 amp 480/277 volt four wire system because all of the heating elements were 277 regulated by an sscr.
 
It would probably help immensely to know what this 'new product' is and what the loads are. Sounds like you are in a design phase. Generally a good OEM will plan for different power conditions in the design when practical.
 
cowski said:
Thanks! That gives me an idea. Yes I've heard that lighting often uses the same 3Ø, 4W, 480Y/277 that I'm looking for...

For a building with 3Ø, 4W, 480Y/277, is there a separate transformer to get 240 single phase? Or wold the transformer have additional taps for single phase 240V?

I'm assuming all buildings with 480 will have 240 single phase as well. If it's a high leg delta with no center tap then I won't get my 277...

Just curious where the 240V comes from if power into the building is 3Ø, 4W, 480Y/277...
Click to expand...
That’s a center tapped delta.
Look up a 480Y/277 bank
 
If I can ask, what kind of equipment is this? May help gauge what kind of facility it will go in. 99% of the services I deal with are 480/277V.

And if you do end up requiring a neutral, make it abundantly clear to the customer.
 
Thanks again. This is a magnetic separator. Our panel is pretty small (7.5kW, <20A). The main load in our panel is a Meanwell DC power supply that uses 3 legs of 277V (that's the main power draw in our panel). It should be a balanced 3 phase load. There shouldn't be much current flowing through the neutral wire, but it will be sized the same as the power wires so it can trip the circuit breaker if there's a phase to neutral fault.

I've talked with our first customer extensively - I think he's actually an electrician. He assured me that he has a neutral with 277V to each leg.

I'm mostly thinking about other customers. The plan for anyone without a neutral would be to install a small isolation transformer, or the DC power supply can accept 208/240 delta without a neutral.
 
Our customers are industrial processing plants... they always have 480V.

It seems hard to reduce 480VAC to 100VDC without a transformer just due to physics. 480VAC rectifies to 678V peak to peak...and then a switching power supply has trouble getting that down to 100V...and they want us to be able to run the magnet at half strength as well (down to 50V).

We may be able to get magnets rated for a higher DC voltage - that may help.
 
cowski said:
Thanks again. This is a magnetic separator. Our panel is pretty small (7.5kW, <20A). The main load in our panel is a Meanwell DC power supply that uses 3 legs of 277V (that's the main power draw in our panel). It should be a balanced 3 phase load. There shouldn't be much current flowing through the neutral wire, but it will be sized the same as the power wires so it can trip the circuit breaker if there's a phase to neutral fault.

I've talked with our first customer extensively - I think he's actually an electrician. He assured me that he has a neutral with 277V to each leg.

I'm mostly thinking about other customers. The plan for anyone without a neutral would be to install a small isolation transformer, or the DC power supply can accept 208/240 delta without a neutral.
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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.

I'd highly question that selection when 1P of 480V would serve the loads cheaper and easier. Most SMPS today are variable voltage inputs.
 
cowski said:
The main load in our panel is a Meanwell DC power supply that uses 3 legs of 277V (that's the main power draw in our panel). It should be a balanced 3 phase load.
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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…
 
Thanks Jraef! That's a lot of good information.

Jraef said:
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.
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This makes sense. Here is the datasheet for the power supply if anyone is interested... I'm guessing they're rectifying each phase separately so it's three separate supplies inside (?).
1752165017414.png
 
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