2 or 3 pole transfer switch

I am installing a 4 wire11kw generator.
Is it preferable to use a 3-pole transfer switch.
If so, why?
Thanks
Reply to
LJS
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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.
Reply to
Gerald Newton
| 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?
Reply to
phil-news-nospam
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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Reply to
Brian
| 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.
Reply to
phil-news-nospam
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.
Reply to
SueMarkP
It is a single phase hookup. My question is:how many pole transfer swtich to use? How to bond the system correctly?
Reply to
LJS
| | |>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)?
Reply to
phil-news-nospam
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.
Reply to
Gerald Newton
maybe its a 220v 3 wire and he is counting the ground as a 4th wire?
Reply to
Bob Peterson
|
|> |> |> >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.
Reply to
phil-news-nospam

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