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wire girl 09-26-2009 11:27 AM

fan forced wall heater
 
Hello, I would like to know about wiring a dimplex rdh series 2000w 240v wall heater. Can I hook up two heaters to one source of 220 wiring?

darren 09-26-2009 01:53 PM

Yup you can wire them together. 4000/240=16.6A.

In Canada you can wire to the calculation, which would be #12 wires. According to our codes we have to bump for the breaker which would make it a 30A breaker. The USA is probably differnet, but someone should chime in and say how they do it in the USA.

It depends on how your thermostats are hooked up, if they are built in you have to take a feed to the first heater, and then a feed from the first heater to the second heater.

If the stats are wall mounted there are numerous ways to do it depending on the layout of everything and which way will use the least amount of wire.

micromind 09-26-2009 05:51 PM

4000 watts at 240 volts = 16.6 amps. This is technically a code violation. It is done around here on a very regular basis though. There is no hazard involved, just a technical violation.

I've connected plenty of 4000 W loads to 20 amp breakers, had them inspected, and all have passed. Only an inspector with a '10 pound badge' would fail this installation.

Rob

Yoyizit 09-26-2009 07:25 PM

And each heater may only need #14 wire 'cause it only carries 8.3A,
HT#1 ----AC-----HT#2

unless you daisy chain the heaters.

AC---HT#1----HT#2

micromind 09-26-2009 07:58 PM

Codewise, about the only time smaller wire is allowed is with motors, A/C units, and welders.

I realize that the load is smaller, and #14 would hold up just fine for the next several hundred years, but I'd use #12.

Rob

Yoyizit 09-26-2009 09:01 PM

Quote:

Originally Posted by micromind (Post 332968)
Codewise, about the only time smaller wire is allowed is with motors, A/C units, and welders.

I realize that the load is smaller, and #14 would hold up just fine for the next several hundred years, but I'd use #12.

Rob

One of these days I'm goin' to have read up on this new-fangled "code" thing everybody talks about. . .:laughing:

Scuba_Dave 09-27-2009 06:02 PM

Quote:

Originally Posted by Yoyizit (Post 332959)
And each heater may only need #14 wire 'cause it only carries 8.3A,
HT#1 ----AC-----HT#2

unless you daisy chain the heaters.

AC---HT#1----HT#2

With a 20a breaker you are saying to use #14 wire??? :no:

Yoyizit 09-27-2009 06:15 PM

Quote:

Originally Posted by Scuba_Dave (Post 333275)
With a 20a breaker you are saying to use #14 wire??? :no:

You're right, that's wrong. :(

007brian 09-27-2009 07:57 PM

Heating units
 
The NEC requires that conductors supplying fixed electric space heating equipment be rated 125% of total load. So 16.4 amps x 1.25= 20.75 amp. Need # 10 conductors.

micromind 09-27-2009 11:18 PM

True enough, but as I stated earlier, I don't know how many times I've connected 4000 watts to a 20 amp 240 volt circuit, had it inspected, and passed. I think very few inspectors are nit-picky enough to fail this installation.

There are code violations that are simply too technical to go after. Most inspectors know this, and are reasonable with minor items.

Rob

P.S. If you want to get ultra-technical, there are two heaters. Each heater draws 8.3 amps. 220.5 (B) states "Where calculations result in a fraction of an ampere that is less than 0.5, such fractions shall be permitted to be dropped."

Therefore, the result of the calculation is exactly 16.0 amps. 16 X 125% = 20. A 20 amp breaker is indeed compliant.

007brian 09-28-2009 07:58 AM

Calculations
 
Any 20 amp stab in circuit breaker is rated at 80%. A 20 amp breaker will trip at around 16 amp. It is not only not compliant, it won't work. Regarding dropping the .5, when you do the calculations and the load is 20.75, you cannot drop anything, .75 larger than .50. In other words,if the total branch circuit load is 20.5, the .5 can be dropped. On a practical note, no professional electrician would suggest or install this with #12 wire. I don't believe in " it works so it must be right". We go by the NEC which, in our trade, is adopted as a legal document. I cannot tell you the number of times DYI'S have done non-complaint installations and created problems. I prefer not to be part of it.

HouseHelper 09-28-2009 08:04 AM

Quote:

Originally Posted by 007brian (Post 333482)
Any 20 amp stab in circuit breaker are rated at 80%. A 20 amp breaker will trip at around 16 amp.

Not true. A 20A breaker will carry 20A for quite awhile without tripping.

jbfan 09-28-2009 09:12 AM

Quote:

Originally Posted by HouseHelper (Post 333483)
Not true. A 20A breaker will carry 20A for quite awhile without tripping.

Agreed!

007brian 09-28-2009 09:25 AM

Breaker size
 
I had a job inspected and I had 18 amps on a 20 amp breaker. Inspector turned it down. I fought but lost. Asked Cutler Hammer Rep and he told me all stab in c/b's are only rated at 80%. That's what the inspector giged me on. That's where this thought comes from. Brian

micromind 09-28-2009 09:38 AM

According to the trip curves in my Square D book, a QO120 (20 amp single pole) will carry between 100 and 120% of its rated current for more than 300 seconds (5 minutes). Anything over 300 seconds is considered continuous.

Nowhere do I see any breaker that will trip at less than its rated current.

If a 20 amp breaker and #12s will not work, and considering how many I've installed, where's all my call-backs? Don't you think there'd be at least one?

In over 19 years, there have been zero.

All code is written based on past experience, and local jurisdictions are allowed to ammend it, again based on experience. The obvious experience of the inspectors around here is that 4000 watts on a 20 amp breaker using #12s does not constitute a hazard.

If 220.5 (B) is applied to the load calculations, then this installation is indeed compliant. 8.3 becomes 8.0. 8.0 X 2 = 16.0.

Rob


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