If you used a four pole transfer switch you would have to install a separate
grounding electrode for the generator and the generator would be classified
as a separately derived AC system. This would also require a second main
bonding jumper at the generator. This requires extra time and knowledge.
It is easier to use a three pole transfer switch.
If you want to see some excellent diagrams of grounding these types of
systems go to the last chapter of the IEEE Orange Book for Standby Power
Systems.
There are some excellent diagrams showing current flow when these systems
are improperly grounded.
I am guessing 3 phase but, without seeing the unit I reserve comment. If you
are using
3 phase you want all 3 phases to open and close at the same time for safety
reasons.
| I am installing a 4 wire11kw generator.
| Is it preferable to use a 3-pole transfer switch.
| If so, why?
Is that single phase or three phase?
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| Phil Howard KA9WGN |
| I am guessing 3 phase but, without seeing the unit I reserve comment. If you
are using
| 3 phase you want all 3 phases to open and close at the same time for safety
reasons.
Unless it is a corner grounded delta. A CGD is similar to single phase
wiring, but the two hot wires are at a 60 degree phase angle, which
results in the same voltage between hot wires as between either and
ground. Opening and closing the 2 hot wires is all you need to do.
what remains is like the neutral in split single phase; you leave it
connected (as well as the separate grounding wire).
So, 2 wire switching can be applied to three phase if it is CGD.
But for center tapped delta, which is 4 wire, and wye, which is
also 4 wire, you do need to switch all 3 hot wires, leaving the
neutral and ground still passing through.
Split single phase only needs 2 wires switched. I worry that some
people might think 3 need switched.
Do you have to, or is it just an option? Can't you just use 2 poles if you
want to or use a combined neutral/ground if desired? If this is a 120/240V
single phase generator, a 3 pole switch allows you to install the generator
both ways (separately derived or not separatetly derived). Where this
matters is in the generator bonding. If you cannot unbond the generator
neutral from the generator chassis, then you run 3 wires from the generator
and switch all three simultaneously. The generator must have a ground
electrode in this case too. If you can unbond the generator neutral from the
chassis, then a 2 pole switch is all you need, but you must run 4 wires
keeping the neutral and ground isolated (but you don't switch the neutral or
ground). The ground electrode in this case is your main power service
ground.
If you install the transfer switch right at the electrical service, and the
switch is rated "suitable for use as Service Equipment", then a 2 pole
switch can always be used since you leave the generator bonded. Only at the
service can the neutral be both grounding and grounded conductors.
| |
|>I am installing a 4 wire11kw generator.
|>Is it preferable to use a 3-pole transfer switch.
|>If so, why?
|>Thanks
| It is a single phase hookup.
| My question is:how many pole transfer swtich to use?
| How to bond the system correctly?
I'm assuming you are in North America.
A 4 wire generator sounds like one with 2 separate windings to allow you
to choose either 120 or 240/120. How you should hook this up depends on
what use you are making of it. If you have one load that needs 120 volts,
wiring it in parallel would make sense. Since you are talking about a
transfer switch, and the fact that 11kw is a lot for a 120 volt load, I'd
guess more likely you are powering several loads in which case you will
need the 240/120 arrangement.
You need to switch the hot conductors. Whether you also should switch the
neutral depends on whether the generator is to be treated as a separately
derived system. If you don't have a need for that, I don't think you
should have that, in which case the neutral would not be switched and you
would use a 2-pole switch (1-pole for the unlikely case of 120 volt only).
How are you grounding the generator? Where is the transfer switch in
relation to the utility service entrance and the breaker panel(s)?
So you have a four wire single phase system.
This is new one for me. Please disregard my previous post.
I have heard of 3 phase four wire, one phase three wire, but a single phase
four wire....
How is the generator wired?
Perhaps you can shed some light on this subject.
|
|> |>
|> >I am installing a 4 wire11kw generator.
|> >Is it preferable to use a 3-pole transfer switch.
|> >If so, why?
|> >Thanks
|> It is a single phase hookup.
|> My question is:how many pole transfer swtich to use?
|> How to bond the system correctly?
|
| So you have a four wire single phase system.
| This is new one for me. Please disregard my previous post.
| I have heard of 3 phase four wire, one phase three wire, but a single phase
| four wire....
| How is the generator wired?
| Perhaps you can shed some light on this subject.
Generators typically have 2 wires per winding brought up to the terminal
box. This allows maximum flexibility (along with exciter tweaking) to
select just about any voltage you want. Smaller single phase generators
might have just 2 windigs. If they are 120 volt, you could wire them in
series for 240 volts (in this case 45.833 amps), even with a center tap,
or in parallel for 120 volts only (91.667 amps). This might be what he
is referring to by "4 wire11kw generator". A 3-phase generator with two
windings per phase (6 total) would be a 12 wire generator.
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