How hot can an electrical plug safely get

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jac

jac

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Originally had this issue raised earlier in May after we slept aboard and left a 2KW heater plugged in overnight. In the morning, the plug was slightly warm which concerned me. One thing on the list to check out over the winter. (Not using electrical heaters on board over the summer!)

The shore power is the one installed by beneteau when built so assuming was specified ok and no visible damage to anything.

However since then I have noticed a number of other plugs in all sorts of locations that are above ambient temperature. Is this normal and I've never noticed in the last 40 odd years or am I suddenly blighted by either extreme sensitivity to warmth or a lot of dodgy wiring wherever I go.
 
The plug on our 2kw fan heater also gets pretty toasty. Even managed to melt a plastic piece on the socket. :eek:

These days I make sure the fan is not blowing air anywhere near the socket, it really doesn't need any extra heating!
 
jac said:
Originally had this issue raised earlier in May after we slept aboard and left a 2KW heater plugged in overnight. In the morning, the plug was slightly warm which concerned me.
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Is this a square-pin 13A plug or a round-pin continental type?
 
Good plugs and sockets, correctly wired, should not get hot even with 13A going through them. I have had a few fail over the years, and it has always been because of a bad wiring connection inside. I think it would be worth opening both bits up and having a look.
 
jac said:
The 2kw heater was a standard 13A square but was plugged in via an adaptor to one of the continental ones.
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Ah! Adaptors aren't often the best engineered bits of kit, was the adaptor warm as well? You could try putting a proper continental plug on the heater cable, or you could change the socket for a 13A type. Get the best products you can - MK is a good make.
 
I had one get very hot and it was due to a bad connection in the plug so was acting like a resistive heating element. Re-did the connections and it was much better it but still got very slightly warm to touch when using the heater at 2Kw so maybe it was not perfect.
 
JumbleDuck said:
Good plugs and sockets, correctly wired, should not get hot even with 13A going through them. I have had a few fail over the years, and it has always been because of a bad wiring connection inside. I think it would be worth opening both bits up and having a look.
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neilf39 said:
I had one get very hot and it was due to a bad connection in the plug so was acting like a resistive heating element. Re-did the connections and it was much better it but still got very slightly warm to touch when using the heater at 2Kw so maybe it was not perfect.
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Precisely.

If the plug is correctly fused, and propely and securely connected, it should never get warm.

The usual cause of a warm plug is a loose screw on the live or neutral pin.
 
It should not get warm at all, check the tightness of the terminal clamps inside and that there's no corrosion as corrosion will cause heating up. Rubbish/underspecified cable, loose clamps and corrosion cause 99% of the problems here, with the other 1% being poor quality plugs that just don't meet the BS standard and are dangerous.
 
Don't use 13A to Shuko adaptors with high powered appliances. They are often of poor quality and more suited to intermittent low power use.

Rewire the heater if competent to do so with a decent Shuko plug.

http://cpc.farnell.com/_/90401/schuko-rubber-plug/dp/CN06990

That rather assumes the socket is of a suitable quality.
 
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The most likely cause is a loose screw terminal. It could also be a loose fuse, sometimes the clips open up a bit. It's worth opening the plug up and checking.

The reason a plug can get hot is because the power P dissipated by a connection is P= I x I x R where I is the current and R is the resistance of the connection, so with something like a heater taking nearly ten amps you only need a resistance of a tenth of an ohm across the connection to give ten watts. In a closed plug that will soon get warm. Because a tenth of an ohm only drops one volt at ten amps the appliance will still seem to work fine.
 
It could also be a poor contact between the pins of the plug and the socket. Hence this thread:

nigelmercier said:
Has anyone found a source of UK BS1363 (13A mains type) plugs with tinned or plated pins? Many leads come with such plugs moulded on, but I've yet to find a source of rewireable plugs.

[Later] I don't mean the gold or silver types for audiophiles, just Nickel plated ones that won't tarnish.
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I have never understood why Benny and other builders (or at least UK dealers) do not change the things over. I often swap them over for the 13a square pin equivalent for customers who complain about just your problem when used with adapters and high current devices even on nearly new boats (including my own) They are a straight swap over and easily available at a fiver or so each http://www.furneauxriddall.com/acatalog/13A-Socket-Outlet--White-BK_09_6262_25_02.html#SID=235
 
David2452 said:
I have never understood why Benny and other builders (or at least UK dealers) do not change the things over. I often swap them over for the 13a square pin equivalent for customers who complain about just your problem when used with adapters and high current devices even on nearly new boats (including my own) They are a straight swap over and easily available at a fiver or so each http://www.furneauxriddall.com/acatalog/13A-Socket-Outlet--White-BK_09_6262_25_02.html#SID=235
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Exactly. Quick and easy to replace.
 
David2452 said:
I have never understood why Benny and other builders (or at least UK dealers) do not change the things over. I often swap them over for the 13a square pin equivalent for customers who complain about just your problem when used with adapters and high current devices even on nearly new boats (including my own) They are a straight swap over and easily available at a fiver or so each http://www.furneauxriddall.com/acatalog/13A-Socket-Outlet--White-BK_09_6262_25_02.html#SID=235
Click to expand...

Now that is very interesting. Had never really considered that they could be replaced with something that is a direct fit. Thank you very much.
 
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