Transformer 240VAC Secondary Wiring

the one tackles with delta secondary..the other is wye...that's why.

The hook up were neather leg is ground is called floating were if you have a hold of eather leg of power you won't get a shock. This is usede a lot with electronic curcuits. Both ways will work. if floating it is a little harder to trouble shoot when you have a problem.

Mining company will ground one phase on 3 phase system so they don't have to run a 3rd wire to the equipment.

For the devices that show both legs hot, is there a reason that they both have to be hot (ungrounded)?

Since 415/√3 ≈ 240, maybe you don't need a transformer. If the control loads are very small, simply use one phase of the 415v supply. If there are many control loads, distribute them among the three phases, as balanced as practical.

This is just an idea; there may be isolation reasons that dictate a transformer. However, a single-phase transformer will also create an imbalance.

Hi Guest,

As you need 240vAC on the secondary terminals(at the load), then you have to connect the transformer secondary as "Delta Δ" ... this way you can get the voltage between every two hot lines is 240v..... On the other hand, if you want to make the delta- connected transformers grounded, then the voltage between a hot line and the inter-ground is 240/2= 120v.

HOPE THIS HELPS.........

above I just tried to explain your query, but I agree with Tornado, as you don't need a transformer if your load requirements are small enough to work without using any transformer,,,, However,that depends on your loads and the purposes of the control circuit you're designing................... please further explanations.

awaiting..........

What is the primary consist of 120/208-120/240 3 Phase or single phase 220

A lot of German machines that I see coming to Canada have enormous ground wiring to a central ground terminal strip. Then they do not ground the secondary of the transformer. Apparently it is up to the local authorities to decide if to ground or not.

Here in Canada the secondaries are always grounded. This serves the main purpose of; if the non grounded line is accidentally grounded thru wear or fault then the secondary fuse will blow.

If the secondary is not grounded (floating ground) then if some one fault grounds the other leg, nothing happens. If another fault then grounds out some where else then you end up with a crossed circuit with really fun and weird things happening.

I prefer to find a single ground fault rather then find muliple faults happening at different times.

You Got it. 240 volts single wire with transformer generated nutral that can be tied to any grounding source. Note you can not creat a nutral for the 240 volt circuit ungrounded conductor.

Cole Bene

Hamdi Hiyari, Electrical Engineer Power Division/ since 1980:

The controls will function in the two cases, due to safety regulations earthing of one of the transformer's sides to earth is mandaory will result in better lifesafety protection.

Regards,

Haven't done any German equipment yet, but have done machinery for Ireland, England, and France. All equipment we have wired here for European markets using 240VAC have a neutral that is tied to ground. So far, all the customers we have built equipment for expect a fuse block for the neutral side, but insist on a solid (dummy) fuse in this line. If you left the one side float, that dummy fuse would be a big problem. Better tie on side of the transformer to ground and call it neutral. That is what their maintenance electricians will be expecting - a grounded neutral and a 240V line.

Hi Guest,

what you will get in Germany is 400 V (+/- 5%), if this is close enough to 440 V you won't need a transformer. But you are normally not allowed to ground the "neutral", which is kept floating and in fact is called "Mp" (~middle phase). Check te local code!

brgds

Snel

Hello,

I did not work on this issue so far but as soon as I read your letter I remembered the SCOTT CONNECTION. You can try at WIKIPEDIA with the keyword `SCOTT T-TRANSFORMER`. You can try at `www.allaboutcircuits.com` with same keyword.