voltage question

[mickeyrench]

i have a customer who wants a three phase 220v outlet for a reefer truck outside. he has three phase 240v red leg service. in his electric room he has a transformer from 240v delta to 208/120v y. i took a voltage reading at the trans and it only had 200 v between any two leads and 115 to xo. why would trans only read 2oo volts??. use 2 different meters. the trans has 216v as the lowest tap why? when its 208

 

[barbeer]

I would pose that question to the utility, all voltages are generally nominal meaning 240v may really be 233............

 

[infinity]

The tap on the 240-208Y/120 volt transformer should be changed to provide the proper secondary voltage. Since you're 5 volts low on the 120 and 8 volts low on the 208 your tap settings are incorrect.

 

[LarryFine]

i have a customer who wants a three phase 220v outlet for a reefer truck outside. he has three phase 240v red leg service.

This is fine for a 3-ph load w/o a neutral. Other than coloring the high leg orange, treat it like any other 3-ph supply.

 

[jim dungar]

i have a customer who wants a three phase 220v outlet for a reefer truck outside. he has three phase 240v red leg service. in his electric room he has a transformer from 240v delta to 208/120v y. i took a voltage reading at the trans and it only had 200 v between any two leads and 115 to xo. why would trans only read 2oo volts??. use 2 different meters. the trans has 216v as the lowest tap why? when its 208

It is likely that the refer equipment is rated for a 240V 3 phase service (unless it was intended for a non-US power system). You should be able to supply it from the 240V "red leg" service without a transformer.

Many people (especially non-electricians) still say 110 and 220V, instead of 120 and 240V, even though these have not been standard voltages for more than 40 years.

Most utilities are allowed to supply nominal voltage +/- 5%. This means a 208V service can really be as low as 197.6 or as high as 218.4V and still be normal. Then there is the acceptable voltage drop from the facility wiring (usually another 5%). But regardless per the NEC we should always call it 208V.

Based on your 208Y/120 transformer giving you 200Y/115, I would expect that its input voltage is only 230V.