L-L vs L-N - Does it matter?

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I am designing the power distribution for our equipment that we manufacture and is used worldwide. As such I am using a multi-tap Delta-Wye transformer.

I was wandering if there is an advantage of using Line to Line voltage connections to the loads over using Line to Neutral connections?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
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Electrical Contractor
I would say that's up to the loads to be served. The voltage must be correct whether or not you choose to bond one circuit conductor.
 
I can have the transformer made to supply the voltage in either scenario. I didn't know if there was a reason for choosing one over the other as I can set it up either way.
 

hillbilly1

Senior Member
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North Georgia mountains
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If I understand your question correctly, with L-L wire size could be reduced over the L-N wire size, if your operating at a higher voltage, Which depends on the load, also reduced would be voltage drop if the same wire size is used. Depends on what kind of load you have.
 

infinity

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I can have the transformer made to supply the voltage in either scenario. I didn't know if there was a reason for choosing one over the other as I can set it up either way.


Will the separately derived system be permitted to operate as an ungrounded system? If so it wouldn't really matter much since the load won't really care if one conductor is grounded or not.
 
The voltage supplied to the load is the same in either case.

Based on this I don't think the wire size reduction or voltage drop would be improved.
 
Will the separately derived system be permitted to operate as an ungrounded system? If so it wouldn't really matter much since the load won't really care if one conductor is grounded or not.

I'm not certain what you mean by the SDS permitted to operate as an ungrounded system.

If you are simply stating that if the load allows a Line to Line connection or a Line to Neutral connection then yes it can.
 

nakulak

Senior Member
if its a 3 phase system I could see where L-L connections might make your equipment more easily configurable to different systems; otherwise, without the particulars, I can't see where it would amount to a hill of beans (unless there are voltage requirements you didn't mention)
 

infinity

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I'm not certain what you mean by the SDS permitted to operate as an ungrounded system.

If you are simply stating that if the load allows a Line to Line connection or a Line to Neutral connection then yes it can.


I was asking if your transformer is permitted to operate as an ungrounded system. The load doesn't care either way.
 

gar

Senior Member
Location
Ann Arbor, Michigan
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EE
081116-1053 EST

Here is an example:

HAAS Automation designs their CNC machines as a 3 phase delta, 3 power wires and 1 ECG wire. The newest machines have one main power DC supply that outputs 325 V DC. This supplies the main spindle motor and the servo drives. Fundamentally it is a 6 phase rectifier providing an output ripple frequency of 360 Hz.

Most other motor loads are 3 phase (coolant and chip conveyor).

All low voltage power stuff comes from a single phase control transformer supplied from a pair ot the 3 phase lines.

Noise filtering includes a connection to the EGC (machine chassis).

Thus, the machine can be used on either a delta or Y source. With larger capacitors in the DC power supply or reduced output power capability some of the machines can be used on single phase.

My thought on a system of this type where there are a number of machines running simultaneous is to have a 324 V battery bank for a number of the machines. This accomplishes two things. First, float thru minor power dips. Second, good recovery of regenerative energy instead of dumping it to resistors.

.
 

jghrist

Senior Member
I am designing the power distribution for our equipment that we manufacture and is used worldwide. As such I am using a multi-tap Delta-Wye transformer.

I was wandering if there is an advantage of using Line to Line voltage connections to the loads over using Line to Neutral connections?
As indicated by others, it depends on the loads. Your later posts indicate that all loads are connected three-phase with no neutral or single-phase line-to-line, so a neutral is not required. You would only need the neutral if you had line-to-neutral connected loads.
 

mxslick

Senior Member
Location
SE Idaho
I have a screening room with German-made (Kinoton) film projectors, which were originally designed for 208-240 L-N connections that have been running just fine here in the US at 208 volt L-L connected. The room has been in operation for 11 years.

There have been absolutely no issues at all because of the L-L connection.

Unless there is something in an equipment's design or configuration that places, oh, say a filter with insufficient voltage rating to handle the L-L voltage, there should never be an issue with L-L operation of equipment as long as the L-L voltage falls in the allowable range for that equipment.
 
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