# electric heater

Discussion in 'Electrical Forum discussion & Blog' started by DIY, Jan 6, 2010.

1. ### DIYMember

Joined:
Dec 24, 2006
Location:
Florida
This heater I have is rated at 1800 watts. Before i plug it In I would like to know if the older wireing system here will be able to handle it (positive and negative wires only in any one outlet). What is the best way to figure for that ? Every outlet in this place is a GFCI (Bdrms.,living room,kitchen and 1 in bathroom) or will this type of outlet trip if to much or not enough juice Is detected at outlet ? Thank you

2. ### arfellerMember

Joined:
Aug 25, 2007
Location:
Port Angeles, WA
It sounds like it would be close

Without knowing more about the wireing in the home it is difficult to answer.

However, somthing that might help is

Voltage X amps = Watts

So, Amps = Watts / Voltage

1800 watts/120 volts =15 amps. Normal household circuits will be 15 amps.

You would be pulling 100% of the circuits rated capacity if it is a 15 amp breaker with just the heater alone.

Next you can look at the gauge of the wire. If it is 14 gauge then 15 amp is the max amp allowed.

12 Gauge could carry a 20 amp circuit.

I know this does not exactly answer your question but might help

4. ### ThatguyHomeowner

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Aug 27, 2008
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A bounty hunter like in "Raising Arizona"
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MD
If you have a voltmeter, measure how far the voltage drops when you turn on the heater and post back. A 3vac drop is about normal; that is, from 120vac to 117vac, for example.

5. ### hjModerator & Master PlumberStaff Member

Joined:
Aug 31, 2004
Occupation:
Plumber
Location:
Cave Creek, Arizona
power

The wire size, circuit breaker, and additional load on the circuit will determine whether you can safely use the heater in that outlet.

6. ### Billy_BobIn the Trades

Joined:
Apr 2, 2008
Just curious...

What is the brand / model of the heater and what type of plug does it have on it? (Regular outlet plug?)

Has the plug been changed from the manufacturer's supplied plug?

Last edited: Jan 7, 2010
7. ### jwelectricElectrical Contractor/Instructor

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Instructor
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No .

8. ### Jim PortElectrical Contractor

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Aug 22, 2009
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Electrical Contractor
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How does this help the OP to answer their question?

9. ### jadnashuaRetired Defense Industry Engineer xxx

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Sep 2, 2004
Occupation:
Retired Systems engineer for defense industry.
Location:
New England
Basically, that heater will draw close to a full 15A, and if your input voltage drops below 120 (and your normal may be lower than that), it will try to draw more than 15A, so it is very likely it will trip the breaker or blow the fuse fairly quickly. A constant load like that should have some excess capacityon the supply side. I'd be somewhat surprised if it didn't have a 20A plug on it. This has one of the blades turned 90-degrees so it will only fit into a 20A receptacle.

10. ### ThatguyHomeowner

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It checks connection integrity. Hello again, Mr. Port.

11. ### jwelectricElectrical Contractor/Instructor

Joined:
Jun 14, 2007
Occupation:
Instructor
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North Carolina
This heater will need to be multiplied by 125% or figured at 2250 watts.
The minimum circuit capacity will need to be 18.75 amps.

Most 20 amp circuits in a normal house will trip after a couple hours with a heater this large plugged in.

On any circuit watch for failure of the receptacle that is being used. In most houses all the receptacles are rated for 15 amps and this heater will be drawing the heat of a 18.75 amp load.

12. ### arfellerMember

Joined:
Aug 25, 2007
Location:
Port Angeles, WA
I thought the 125% rule was for calculating sizes for dedicated load circuits like hot water heater.

Why would a 1800 watt plug in heater be pulling 2250 watt load?

Also, why would a 20 amp circuit trip from a 18.75 amp load after couple hours? Heat buildup in the panel?

13. ### jwelectricElectrical Contractor/Instructor

Joined:
Jun 14, 2007
Occupation:
Instructor
Location:
North Carolina
Any resistive load should be figured at 125% weather it is the branch circuit, overcurrent or even a plug and cord appliance.

If a 20 amp circuit has anything else in use with an 1800 watt heater you can count on the circuit opening each and every time, especially after an hour or so.

Any 15 amp receptacle weather used on a multi-outlet 20 circuit or not will fail when more than a 12 amp load is being used for an extended amount of time. This is where a lot of electricians make the statement of not using the stab lock on the back of a 15 amp device comes from.
The tension on the blades of the male plug will start to fail due to the heat of the receptacle.

A small test can be done with this type of portable heater that helps anyone to understand what is happening inside the receptacle. Simply plug in a small electric heater and let it run for about an hour. Unplug the heater and hold the male plug in a closed hand to capture the heat of the male plug inside the closed hand.
If is feels hot then the tension of the receptacle is being lost and at some point in time the prongs of the male plug gets spread apart in order to keep from falling out of the receptacle. At this point the receptacle is failing and needs to be replaced.

I have personally seen where the conductors, yes even the ones wrapped around the screw have started to discolor and melt from the use of portable electric heaters. I have seen many portable electric heaters where the male plug was deformed from the heat produced at that connection point.

Really want to see a problem with portable heaters. Use an extension cord so the heater can be placed closer and then the problems really begin especially from those little brown cords that cost \$1.19 at the local Family Dollar Store.

When the receptacle starts to fail and arcing starts between the blades of the male plug and the tension of the inside of the receptacle we now have an added resistance that is in parallel with the load.

Also in a parallel circuit the total resistance will always be less than the lowest resistor thereby causing more of a load on the overcurrent than the heater itself is pulling.

Should there be a resistance of 25 ohms at the receptacle in parallel with the heater then the 20 amp overcurrent device is maxed out.

14. ### jar546In the Trades

Joined:
Feb 20, 2008
Location:
USA
125% rule applies, no question about that.

Sounds like the OP needs to hire someone who knows what they are doing. Simply not enough information given to give an answer. At minimum a dedicated 20a circuit would be needed for using this heater. If it plugs in, I would suggest a single receptacle and not a duplex.

15. ### jwelectricElectrical Contractor/Instructor

Joined:
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Occupation:
Instructor
Location:
North Carolina

Very sound advice as a single receptacle on a 20 amp circuit would require a 20 receptacle.

210.21
(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

16. ### Jim PortElectrical Contractor

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Electrical Contractor
Location:
Maryland
The question was dealing with circuit capacity, not connection integrity.

17. ### ThatguyHomeowner

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A bounty hunter like in "Raising Arizona"
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Connection integrity affects circuit capacity, in non-obvious ways.

Here's a Rorschach-like test for you. For 10 points, referring to my avatar, are you the kid or the snake?

Last edited: Jan 9, 2010
18. ### Jim PortElectrical Contractor

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Occupation:
Electrical Contractor
Location:
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But even with a circuit that is intact there would still be an issue of whether the circuit could support that potential load. I don't know why you feel you must cloud the issue.

Circuit intergrity would effect anthing plugged in. It would just have a greater impact with larger loads. Even a dedicated 20 amp circuit could have issues if there were poor quality connections.

19. ### ThatguyHomeowner

Joined:
Aug 27, 2008
Occupation:
A bounty hunter like in "Raising Arizona"
Location:
MD
What you see as clouding the issue I see as pointing out non-obvious things that may cause trouble, while not rehashing the previous replies. On Internet forums, resi. bad connections seem pretty common, and commonly baffling, to the HO.

There is a book by DV Lindley on Decision Making, and in it he points out the value in listing all possible outcomes of a decision. I use this advice to try to think of all possible problems that may be reasonably encountered.

Neither is easy, listing outcomes or foreseeing problems.

Last edited: Jan 9, 2010
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