460/3/60 with neutral

[brinkmann27]

I know that 230/3/60 with a neutral can provide 115/1/60 (L1 with neutral). Is there or can 460/3/60 with a neutral provide 230/1/60 ? (L1 with neutral)

Thanks

 

[dpc]

A three-phase 240 V service that also provides 120 V single-phase is a "wild-leg delta" system that has a center tap on one of the three delta windings. It has very limited 120 V capability and is generally a pain in the neck.

It would be possible to create an equivalent mess at 480 V, and provide a 240 V supply. However, this 240V supply would only be 240V - not 120/240V. So instead of 240/120V that is provided by the typical wild-leg delta system, you would have 480/240V.

I've never seen it done, and might not even be allowed by NEC but I'm not motivated enough to look and see.

 

[waross]

Hi brinkman27
I agree with dpc's second and third paragraph completely.
Check NEC!
In addition you may want to check thread 238-143892 before proceding with a Star/Delta, three transformer connection. It may be less time consuming to go to the end and read the later posts first.
As wfowfo pointed out, Rea standards allow the connection with a floating primary neutral. They warn that if the neutral is grounded, transformer burnout may result.
The floating neutral is not allowed in some jurisdictions, and there may be safety issues with lethal voltages on the primary neutral under phase loss conditions.
As stevenal informed us;
The REA is now the RUS

http://www.usda.gov/rus/electric/bulletins.htm

 

[jraef]

But you can easilly find 480/277V 4 wire transformers. that is why a lot of lighting systems are offered with 277V input.

You will not find an off-the-shelf 480 wild leg 240V transformer, even if the NEC says nothing to prevent it. It would be cheaper to just buy a separate 480-240V 1 phase transformer and be done with it.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[mc5w]

In some western states in the U.S. there is such a thing as 240/480 4-wire delta. However, metering needs to be done with 2:1 voltage transformers such as the VT package from

http://www.socket-two-me.com

This is for use with both 200 amp and 20 amp form 9s meters. The 200 amp form 9s meter is a semi-self contained meter for use where voltage transformer but not current transformers are needed.

The primary advantage of 240/480 4-wire delta is that it can be initially installed using 2 transformers and 2 hot wires and a neutral on the primary side. A 3rd transformer and primary hot wire can be installed as the load grows. The same advantage attaches to 120/240 4-wire delta.

Back in the 1960s noise abatement along Interstate 71 in Columbus, Ohio was done by running 120/240 volts 4-wire delta into all of the houses and installing 3-phase air conditioners. I have seen quite a few houses that have 3-phase air conditioning because before about 1967 or 1968 residential central air had to be 3-phase.

If you look in the General Electric Blue Book for revenue metering you will find in some of the back pages a 5-wire service that was both 120 volts 2-wire single phase and 240 volts corner grounded using a form 16A or 16S meter. This was an early proposal for bringing in 240 volts for motors in houses. Early residential refrigerators were as badly behaved a load as an electric arc furnace until somebody figured out that a 4-pole induction motor driving 2 cylinders was the power quality problem. Hook up a Campbell & Hausfeld Power Pal to a weak power system and it makes the lights blink like in a discotech.

 

[tommom]

Also be careful about applying circuit breakers on such a transformer - the max voltage to ground will be more than 277 volts, it will be 240x1.73 = 415 volts.

 

[brinkmann27]

Thanks for all the replies.....if the customer is correct and the line to neutral voltage is 240 volts, not 277 what is the proper way to add circuit breakers? This is a 3 phase system. The 480 volt ones are no problem, a standard 3 pole 600 volt breaker. But if we use a line to neutral connection for 240 volts, do you use a single pole breaker and connect the neutrals straight thru? Or do you use a 2 pole breaker and break the line and neutral legs?

Thanks again!

 

[waross]

It's basically the same as a 120, 240 volt system.
For a 240 volt load use a single pole breaker and neutral.
CAUTION THERE WILL BE A WILD LEG WITH 416 VOLTS TO NEUTRAL. YOU MUST CONNECT 240 VOLT LOADS TO ONE OF THE OTHER PHASES.
For a 480 volt load use a two pole breaker.
If this is a closed delta system the two pole breaker may be used in any position. But it is good practice to avoid the wild leg for all single phase loads.
IF THIS IS AN OPEN DELTA SYSTEM IT IS GOOD PRACTICE TO AVOID THE WILD LEG FOR ALL BUT THREE PHASE LOADS.
Many open delta systems have a smaller transformer feeding the wild leg. The transformer may be sized for the existing three phase loads only.