[pilotarix]

Hi all,

This might be a no brainer for all of you but 240v split phase is relatively new for me.
I have a CNC enclosure that requires 240v for the VFD. Now I would like to install power outlets (120v) for the control computer and the cooling pump.
The cable to the enclosure is a four conductor cable - 2 hot - neutral and ground.

How to get 120v out of the 240v? Do I need a step down transformer or can I “just” use one phase of the 240v?

Thanks for your input.
Christoph

[joeavaerage]

Hi,
no transformer required. One phase to the neutral is 110VAC while the voltage between the two phases is 220VAC.

Craig

[pilotarix]

Craig,

Thank you for your reply.
I wasn't sure if it was really that simple. I saw some examples where a step-down transformer was used to get the 110VAC. Could it be that you have to use a transformer if you don't have a neutral?

[WesM]

You should have 4 wires coming to the enclosure, two 120vac hots, a neutral and a ground. The two 120vac legs give you 240vac. To get 120vac you will use the neutral and a single 120vac leg.

[joeavaerage]

Hi,

Could it be that you have to use a transformer if you don't have a neutral?

Yes.

In New Zealand we get 240VAC single phase. That is to sat I'd have only three wires into the machine, one phase, one neutral and the earth. If I needed 110VAC I'd have to use a transformer......
although why I'd bother with 110VAC???

Our three phase ie three 240VAC phases which results in 415VAC between any two phases. Sure does make equipment sit up and take notice!!!!

Craig

[RaderSidetrack]

Craig,

Thank you for your reply.
I wasn't sure if it was really that simple. I saw some examples where a step-down transformer was used to get the 110VAC. Could it be that you have to use a transformer if you don't have a neutral?

Note that the solution presented in post #2 puts all of the load of the 110/117VAC circuit on one leg of the 'hot' pair.

While that may not make a difference, depending on the wire capacity rating and the breaker size, it MIGHT become a problem. The paired breakers in the panel are likely mechanically interlocked, and if one trips the other will too. Since the proposed solution puts all the load on just one of those breakers, the "margin" of available amps until the breaker trips will be less than if the load was spread across both breakers (via a transformer etc). A transformer would split the "added" amps over both hot legs.

So, depending on the wire sizes, breaker sizes, the amperage load at this point, and the future added amperage to the single leg, it could be better to use a transformer.