# Do I have 208 or 240 volts in my apartment?

• posted

I just had a new circuit installed for a dryer. I was told it was 240 volt but I'm having doubts. Would I be able to tell from the panel? The following is an excerpt from my building's electrical specifications. The building has 10-20 apartments:

"From a service end box, electrical feeders connect to a service switch which provides power to the building?s residential systems. The service switch is a three-phase, four-wire 208/120 volt switch rated for 600 amperes. The service switch conducts power to the residential electrical meter bank. Each residential unit is provided with a dedicated feeder Each dedicated feeder then conducts power at one-phase, three-wire 208/120 volt to local distribution panelboards located in each residential unit."

Sounds to me like I can only get 208 volts, but if power to my unit is only provided at one phase, I'm confused as to why it would be 208 volts, which I thought was a voltage between phases.

Is it even possible for me to have a 240-volt circuit in my unit based on the above description?

• posted

It sounds like you have single phase 120/208 derived from 3 phase wye. It is not uncommon in multifamily. The only way you would get 240 is if the building was wired 3p center grounded delta and that would be rare in your situation. Your dryer should work, that answer is in the electrical requirements in the installation manual but it will dry slower.

• posted

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So in the US sometimes you have low voltage wired in wye and sometimes in delta? because here it's always wired in wye with center grounded,

230/400 volt. Usual service is 35 A, 230 Volt. Sometimes bigger houses are 3 phase 400 volt but usually have no 3 phase load, just 1 phase loads distributed across 3 phases. Usually 3X 35 A, 400 Volts. Usual 3 phase loads in industry are of course induction motors and heating elements etc. but it's still 400 Volts (not 660 it's very unusual).
• posted

I really doubt the drying time will be noticeably slower, if at all.

• posted

Typically they want the ability to derive 120v single phase on a general use service so you can end up with 240, center tapped delta that will give you the full 240v across the line to line loads and on one winding you get 120/240 center tapped like the normal single phase service. In fact that is exactly what it is. They use a large single phase transformer for the 120v loads and add a second one for the 3d phase. It lets them provide 3p with two transformers but you usually see that in a light industrial application where they need some 3 phase along with a normal 120/240 service. It is known as "Delta Vee" or Red Leg Delta because that 3d phase is 208 above ground. You also need to derate the current because of the missing leg and you should not really use line to neutral loads on the 208v leg. It is for pure 3 phase loads like motors.

The other common service is 3 phase wye with 208 between phases and

120v line to neutral on all three. That is better when you are using a lot of 120v and willing to compromise on the 208 line to line. It does require 3 transformers tho.
• posted

The power (watts/BTU) decreases as the square of voltage. That 32 volts will be missed on a toaster wire heater like a dryer. (Like about 75% of the rated output). The motor and controls generally run line to neutral so it will still be 120v for them.

• posted

The temp of the dryer air is regulated to not get too high. Yes, 240v wll get the elements hotter, quicker, but then they will most likely get cycled off to keep from getting the air too hot. I am talking about drying time, not heating element temp. Don't forget to keep the dryer exhaust venting pipes clean.

• posted

Excellent point. I suppose it would only be important when they were running flat out, like a big load of towels. You are right. Most folks might not notice.

• posted

yeah you are right

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