On Dec 10, 9:00 pm, (Doug Miller) wrote:
In article . com, "Terry" wrote:

I admit I don't know, but I would think instead of going to #10 and a
30A circuit you would be required to run 2 separate 20A circuits if the
total load exceeded 16A.

Why? Is there some reason you think it would not be acceptable to attach a 16A
load to a 30A circuit?


Like I have said, I don't know for sure, but I have it in my head that
if you can limit the load to 15A or 20A then you should.



I would also assume that you would take the the only two choices you
would have. Either the equipment would be 110 or 220. Why would they
sell something that was not the common voltage for the home?

Residential electrical supply in the US and Canada hasn't been 110/220 for
many years -- it's 120/240 and has been for a long, long time. Doesn't stop
people from referring to it as 110 and 220, obviously, but that's not what it
is.

My point was this: the OP referred to installation instructions that said
(according to his post) to connect the equipment to a 220V circuit. Maybe that
was just a mistake on the part of the OP and the instructions really said
240V, or maybe they really said 220V like he said -- and if *that* is the
case, that the manufacturer really said 220 and not 240, it's quite possible
that the rated output of the heaters is based on their output at 220, and not
at the 240 that the OP certainly has in his house. And the distinction is
important because if these heaters were rated at 240V, then they can both go
on the same 20A circuit -- but if they were rated at 220V they cannot.

Taking 240V instead of 220V the current would be less and not more.
This would be 14.6A

Wrong.

Take the case of a resistance heater that emits 2000 watts at 220V. It draws
2000 watts / 220 volts = 9.09 amps. Now calculate the resistance: 220 volts /
9.09 amps = 24.2 ohms.

Note that the resistance is a physical property of the heating element, that
does not change no matter what voltage is applied to it.

Now push 240V across that same 24.2 ohm resistance.

240 volts / 24.2 ohms = 9.92 amps.

A similar calculation applies to the 1500 watt heater.


I do understand that if you use somethign designed for 220V and it is
infact 240V the current would be more

Isn't that exactly the opposite of what you said in the previous paragraph?

but can't see that being the
case something designed for a home.

Maybe you're right -- but assuming that, without proof, could be dangerous.
Which is why I cautioned the OP to check the rating plate to see whether the
heaters were rated at 220V or 240V.

I wish the OP woud chime in and give any more information he could give
on the heaters, like maybe the Full Load Amps.

Simply knowing what voltage they're rated at is sufficient.


My assumption for using 240V was that the OP had made the same mistake
we all do in referring to 110-220 and 120-240 interchangeably. If this
was the case, then the load would be 14.6A. Maybe I didn't say that
too clearly, but that would be my observation. I am sure he got the
wattage right, and I would think that he couldn't buy a heater for the
home if it was truly rated for 220V.