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I had an electric water heater installed in my bathroom this morning. It uses a 16A plug but I only have 10A sockets in the bathroom (the only 16A in the apartment is high on the bedroom wall for an AC unit).

I know the hardware store sells powerstrips that can take 16A plugs, and which have 10A heads. The largest is rated to 4000w.

Would this be a safety hazard?

If yes, can I just replace the socket in the wall or do I need to get the whole damn thing rewired back to the fusebox?

ADDITIONAL INFO

  • The heater's plug has a built-in fuse, the kind that pop-up and can be reset, and says 10 mA on it.
  • The heater offers 3 heating modes: 1000w, 1500w, and 2500w (the first 2 are individual heating elements, I assume)
  • I have two breakers for the bathroom. One is dedicated to one outlet, the other to the lights and another outlet. Both are rated 230/400V 50Hz 6000w IEC 60898 GB 10963
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Andrew, we need to know where you're at to be able to answer this question. –  Karl Katzke Sep 10 '11 at 14:56
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@karl: From an earlier queston he's in China, so 220V / 50Hz. Andrew: what is the power rating for the water heater. If it's above about 2kW (220V * 10A == 2.2kW maximum, and you should leave a safety margin), you should get it rewired because you'll be coming close to the rating for that circuit. –  Niall C. Sep 10 '11 at 15:04
    
Niall - Make that an answer so I can upvote it. ;) –  Karl Katzke Sep 10 '11 at 18:26
    
Are you sure that the fuse says 10 mA and not 10 A? There should be a current spec on the breakers as well: could you post it too? Also, if there are any markings visible on the wiring, they would be helpful to add (they'll say what wire gauge it is, which will indicate how much current it can carry). –  Niall C. Sep 11 '11 at 0:24
    
Despite the answers given saying try it, the power source must always be higher rated than the power sink. Power source = socket, power sink = appliance. Sitting around figuring power consumption is goofery, you've been told what the source should be rated at, plugging in an appliance that potentially will draw more than can be supplied by the size of circuit wiring and components will cause a fire hazard when the wiring or the sockets give way. If you're lucky, there will be a fuse or circuit breaker to prevent overcurrent. –  Fiasco Labs Jan 13 '13 at 4:55
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3 Answers

up vote 4 down vote accepted

It depends on the power rating of the water heater. From an earlier question, I see that you live in China, so your electrical supply is 220 VAC/50 Hz. That means that the maximum power draw on a 10 A circuit is 2.2 kW (220 V * 10 A). In general, you should draw less to allow a safety margin, if the water heater uses more than about 2 kW you should get it rewired because you'll be coming close to the maximum rating of that circuit.

Note: I'm not even considering the presence of other appliances on that bathroom circuit (lights, electric razors, electric toothbrush chargers, etc.).

Based on the additional info in the question, if you only use the 1000 W and 1500 W modes on the heater, the existing wiring should be sufficient. If there's a way to prevent people from using the highest setting (like mounting the whole heater in a box where it can't be changed inadvertently), you should be OK.

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hi Niall, I've updated the Q with a bit more details, please review and adjust your answer if necessary –  Andrew Heath Sep 10 '11 at 22:32
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Usually the plug reflects what the wires can safely deliver. Unless a qualified electrician looks at it and says otherwise I would assume it has to be rewired all the way back.

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Current rating on the plug requires that the current rating on the socket and the wiring back to the circuit breaker panel are rated to deliver equal or greater current than the device is rated for. –  Fiasco Labs Jan 13 '13 at 7:25
    
@FiascoLabs: Code requires it. That doesn't mean some moron didn't change things incorrectly, though. –  Loren Pechtel Jan 13 '13 at 21:09
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"Both are rated 230/400V 50Hz 6000w IEC 60898 GB 10963 electrical."

This is three-phase power. Do you have a three-phase water heater? If so, you're fine.

If not, it can be discussed further.

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no, it's not a tankless heater. We originally wanted one of those, but the building superintendent said the grounds area would need to be 4sq m and ours is only 2.5, so it can't support so much current? It's a small tank heater mounted under the sink. –  Andrew Heath Sep 11 '11 at 0:01
    
@Andrew The writing on the breaker very clearly indicates that you have a three-phase wye or three-phase high-leg delta system. See grainger.com/Grainger/wwg/… for examples of three-phase tanked water heaters. If the water heater is using three-phase, it's using 400V, which means it's fine. It depends on how it's wired. Please take a picture of the outlet (plug removed, of course,) the breaker (panel cover removed, preferrably,) and the water heater's label. –  Michael Sep 11 '11 at 1:28
    
I will do so, but not for about 36 hours because we're now out of town on holiday. I'll let you know when it's updated. –  Andrew Heath Sep 11 '11 at 7:20
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