L-L vs L-N --- Does equipment care if the voltage is appropriate

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cottora

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This may be a silly question...But, does equipment "care" if power is L-L vs L-N? For instance, will a 230v motor/computer/etc. run on a 230v L-L system the same as if the voltage is derived from a L-N system? Thanks
 
Not silly at all. I remember reading there is 230v Eu. equipment that "expects" one line to be grounded, as our 120v normally has.
 
electrofelon said:
I would say one should not connect a non grounded conductor to a terminal intended for a grounded conductor.
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This.

As far as power delivered to the load it doesn't matter if you supply line-line or line-neutral. But there are additional considerations other than power delivered to the load. You must also consider the capability of the insulation system and any assumptions about supply conductor grounding.

As a very basic example, consider an ordinary screw shell lamp holder. The large (and often exposed) screw shell should be connected to the grounded conductor. The lamp would function just fine connected Line-Neutral, Line-Line (assuming proper voltage) or Neutral-Line (eg. with the screw shell on the 'hot' conductor), but there would be rather different safety considerations.

Or imagine a lamp circuit where you switch the neutral rather than the hot.

If a load is specifically designed to not care which supply terminal is 'hot', then it shouldn't matter if you supply it line-neutral or line-line. Many computer power supplies are designed in this fashion so that they will function in places that don't have polarized receptacles.

-Jon
 
One other difference that can bite you is in heating equipment, especially commercial coffee pots. The capacitance from element to the body of the unit can be large enough to trip a GFCI unless the capacitive current is balanced between the two opposite polarity legs of the heating element(s). The equipment would be "fine" but the GFCI would immediately trip.

Also some equipment contains surge suppression or RFI suppression elements connected between "hot" and ground. A 240V L-N connection instead of 120-N-120 could
exceed the withstand voltage of the surge suppressors. A supply of two of three from 208Y/120 would probably be OK in this instance, but not in the first paragraph situation.
 
Most of the time this issue comes up around connecting 230V equipment from the EU or Asia where they use L-N for 230V, and you are installing it here where we nave it L-L. In that case, electorfelon's warning is valid. As a general rule equipment froom the EU or built for the EU will be designed like we would; no bonding of ground (earth) to neutral INSIDE of the piece of equipment. But on more than one occasion, I have see stuff from Asia (China) where they did NOT follow that rule; where they DO have a bonding jumper from earth to the neutral somewhere inside of the machine or appliance. You find out right away when the magic smoke is released...
 
A related question. Does it matter if the entire load of a panel/transformer is L-L? We have a 1MVA 208Y transformer and the entire load will 208 L-L with no load connected to neutral (2-pole breakers). I believe that this is ok and we still get the 1.7x amperage rating from the panels to the circuits.
 
If your loads do not require a neutral, your fine! The machine will be very happy being supplied with the right voltage, IMO.
 
cottora said:
A related question. Does it matter if the entire load of a panel/transformer is L-L? We have a 1MVA 208Y transformer and the entire load will 208 L-L with no load connected to neutral (2-pole breakers). I believe that this is ok and we still get the 1.7x amperage rating from the panels to the circuits.
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True only so far as you've balanced your loads across all three phases. With balanced loading you can use the full capacity of the transformer, and don't need a neutral connection.

Not sure what you mean by 1.7x amperage rating, however.

Imagine the extreme unbalanced case and you will see the problem if your loads are not balanced. If you have no other loads, what is the maximum single 208V single phase load you can connect to this transformer? (Hint: it is less than 2/3 the capacity of the transformer even though you have 2 of 3 phases connected.)

Since you describe a large transformer with 208V load_s_ connected via panels, I expect that your installation will be reasonably balanced; but just wanted you aware of the approximation inherent to your question and my answer.

-Jon
 
winnie said:
True only so far as you've balanced your loads across all three phases. With balanced loading you can use the full capacity of the transformer, and don't need a neutral connection.

Not sure what you mean by 1.7x amperage rating, however.

Imagine the extreme unbalanced case and you will see the problem if your loads are not balanced. If you have no other loads, what is the maximum single 208V single phase load you can connect to this transformer? (Hint: it is less than 2/3 the capacity of the transformer even though you have 2 of 3 phases connected.)

Since you describe a large transformer with 208V load_s_ connected via panels, I expect that your installation will be reasonably balanced; but just wanted you aware of the approximation inherent to your question and my answer.

-Jon
Click to expand...
Yes, the load is 750 individual computers spread across the three legs evenly. It should be almost perfectly balanced.
 
yuhong said:
I think in Europe 127/220V three phase was still common until relatively recently.
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Not that I'm aware of. When I started work, and that was over fifty years ago, it was 440/250. Now it is nominally 400/230..
 
GoldDigger said:
One other difference that can bite you is in heating equipment, especially commercial coffee pots. The capacitance from element to the body of the unit can be large enough to trip a GFCI unless the capacitive current is balanced between the two opposite polarity legs of the heating element(s). The equipment would be "fine" but the GFCI would immediately trip.

Also some equipment contains surge suppression or RFI suppression elements connected between "hot" and ground. A 240V L-N connection instead of 120-N-120 could
exceed the withstand voltage of the surge suppressors. A supply of two of three from 208Y/120 would probably be OK in this instance, but not in the first paragraph situation.
Click to expand...


Could a transient trip the GFCI even when the coffee pot is on a balanced supply?
 
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