running two single phase dryers from 3 phase tap

Thread Starter

dellis

Joined Aug 31, 2008
3
Can I legally run 2 - 230 single phase hand dryers from one 230 volt 3 phase tap dryers pull 9.1 amps tap rated at 20 amps.
 

RmACK

Joined Nov 23, 2007
54
Legally, nobody can tell you as wiring rules vary from one country to another & you haven't said where you are. Technically, does the 3 phase tap have a neutral connection (star) or just 3 phases & earth (delta)?
 

PackratKing

Joined Jul 13, 2008
847
Not really.... 230 v. Three phase, gives you equal voltage on all three hot leads .... a 230 - 240 volt hookup, off one [single phase ] breaker, normally feeds one leg [ phase ] to the motor, and the other to the heat coil, each in reality only being 115-120 volt. Check the spec plate on the motor itself. I cannot answer the legality question.

My main uncertainty regarding residential hookup from pole to AC distribution panel, is as follows ::

Are the two hot leads from pole to panel busses, two legs of a three phase grid, which would mean they are 120 degrees apart, or is [ one leg of ] residential power 180 deg. out of phase with the other, or are they both the same phase ??????? Maybe I'd better do some homework !!

Someone with more experience please weigh in ???
 
Last edited:

RmACK

Joined Nov 23, 2007
54
Technical:
Single phase is just one of the 3 phases and the neutral that you are supplied with. A standard single phase power socket is wired like this. He could even stick both from 1 phase to neutral since 2x9.1<20A but it is better practice to try to load the phases as equally as you are able to i.e. drier 1 from red phase to neutral & drier 2 from blue phase to neutral.

In a 3 phase system the phases are 120 degrees apart. In a 2phase system, the phases are 180 degrees apart. The beauty of a 3 phase system is you only need 3 wires (just like 2 phase) if the phases are similarly loaded. In this case the currents cancel, neutral carries no current & may be omitted. This is called delta. Star or Y is where you have the extra neutral wire supplied. 3 phase transformers can be configured to go from delta to star or star to star or even delta to delta.

But the original question was:
Can I legally run 2 - 230 single phase hand dryers from one 230 volt 3 phase tap dryers pull 9.1 amps tap rated at 20 amps.
I am not familiar with the electrical laws of Dellis which is why I simply don't know...
 

Bernard

Joined Aug 7, 2008
5,470
You say 230 V 3 phase. Most 3 p. circuits hot to hot will measure 208 V. Can your dryers handle 208? There is a slight chance that the heater has a low voltage motor in series with heating element, if so prpbably no problem hooking 2 units to 3 leggs of 3 phase. All of the previous replys still apply.
 

vetterick

Joined Aug 11, 2008
35
"Most 3 p. circuits hot to hot will measure 208 V", really? That depends on the transformer, if its 120/240 3 phase (very common) you can only use the 2 phases that are 120V to neutral, if your lost with that statement you need to seek professional assistance (electrician).

The original question was about having 2 appliances on one 20A circuit 9.1A each, theres is 2 reasons that won't fly, according to NFPA 70 (NEC).

#1 each appliance shall be on its own circuit.

#2 you can only load a circuit to 80% of its capacity, 9.1 X 2=18.2 > 20 X .8=16.

So you see this can't be done, now if you live somewhere outside the US, I can't say.
 

thingmaker3

Joined May 16, 2005
5,084
For clarification, I was able to determine the OP is posting from within the US. The NEC does indeed apply.
#2 you can only load a circuit to 80% of its capacity, 9.1 X 2=18.2 > 20 X .8=16.
That drops to 50% for "utilization equipment fastened in place, other than luminaires" if the branch circuit in question also supplies an outlet and or luminaire. May not be the case here, but one never knows.
 
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