On 11/01/2013 08:28 PM, Pete C. wrote:

wrote:

On Fri, 01 Nov 2013 11:56:36 -0500, "Pete C."
wrote:


wrote:


the original plug is in row 7, 20R, while the new one is in row 6, 30R. The new heater is rated at 30 amps.

Thanks to all for their comments and links.

Paul

That 7-20R is for 277v, (the L/N of 480v wye).

Again it would work on 240v but at lower power.

If the original was 277V and they connect a 240V rated heater to it, the
heater will run at higher power and may overheat.

I was thinking the other way, 277 heater on 240v. It is unlikely
anyone would have 277v available anywhere but a heavy industrial
complex or large office building.

Greenhouse heater, not necessarily a small greenhouse, could be a big
farm with 480/3. If the original heater was a 277 rated unit operated on
277 then installing a 240 rated heater on that circuit would be a
problem. If the original heater was a 277 rated unit operated on 240 it
would have been running at less than full power and a new 240 rated unit
operating on 240 would perform better.

Agreed on both points.

The OP needs to figure out what
they really have both for power and for the heater.


Yes... so we've identified the plug on the new heater (NEMA 6-30P) Or
have we? What is the nameplate amp rating on the new heater? 6-15P
looks similar to 6-30P but is physically smaller. 6-15P also similar in
size and shape as 5-15 (standard household 3-wire plug/recep) or 5-20
(similar 20A plug/recep, with the neutral horizontal instead of
vertical) except both current carrying blades are horizontal.

Question is now, what voltage is available at the existing recep, what
gauge wire is feeding it, and what is the amp rating of the breaker
protecting the circuit? Finding a 277VAC recep on a 240VAC circuit
would not be proper, although I am slowly learning to expect things to
not always be correct or code compliant.

nate

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