Immersion heater timer (itself) overheating

[Greengo]

This is an immersion-heater-timer burning out problem.

I have a photo of the damage but have been unable to find a way to include it in this document.

I have installed two 13A Masterplug Mechanical Immersion Heater Timers (one timer on each of two different occasions) in the power supply cable between the on/off switch (about 40cm away) and the water tank (about 50cm away). The immersion heater thermostat is set to about 1/3rd up the temperature range (40-45 degrees?).

The cables are all twin plus earth (T+E) single strand of considerable thickness.

The first timer burned out after a few days and was replaced with a second one. This second one has gone all winter without incidents but has now fallen foul to the same problem.

The visible evidence shows that overheating took place at the connection of the Neutral supply to the timer. The heat was sufficient to melt the solid plastic of the timer. The effect on the cable itself was less obvious but there are signs of overheating to about the first 1cm of the neutral conductor. This seems to be caused by heat transmission from the timer connector where the main source of heat was generated.

All overheating seems to have been confined to the Neutral input connector area of the timer. Although arcing could possibly have occurred, because of the first timer problem I am practically certain that all the cables on the second timer were very tightly connected.

I have no idea if the timing function has been affected.

I am mystified by this double occurrence and would appreciate any help or advice that anybody can offer as to
a) the cause
and
b) how to avoid it recurring.

Many thanks.

 

[davy_owen_88]

When the first timer went did you cut back the damaged part of the cable before you connected the new one? Burnt/scorched/damaged copper has a higher resistance than fresh copper so if you didn't cut back to undamaged cable that's probably the reason the problem has come back.

First time due to loose neutral connection. Second time due to high resistance connection due to manky copper.

Davy

 

[THRIPSTER]

The fact that not only the original but the replacement timers have burnt out indicates that there is probably prolonged overload. Perhaps you should investigate the total load connected and the rating of the timers. Combined washing machine and dish washer switching at night is a common cause for this.

If an overload exists then investigate a timer with a higher rating. Should you be competent then what about a timer in conjunction with a relay/contactor?



Regards

 

[Greengo]

Thanks for that very quick reply, Davy.

Yes, I did cut back to the healthy part of the cable before installing the second timer; so I presume this is not the main reason for the problem.

Thanks again. Hopefully there will be other suggestions form some of you more expert members.

 

[davy_owen_88]

Hmm, could you tell us the rating on the immersion heater? They are usually <13A so shouldn't be a problem but over prolonged use they might get a little too hot.

What size is the cable used?

 

[Greengo]

I'm very impressed with the fast replies I'm getting. Thanks to Thripster for this quick one.

Should you be competent then what about a timer in conjunction with a relay/contactor?

I like the idea of a relay. Can you or somebody give me more specific information on how to go about this.


Many thanks.

 

[Greengo]

Thanks again Davy.

Hmm, could you tell us the rating on the immersion heater? They are usually <13A so shouldn't be a problem but over prolonged use they might get a little too hot.

What size is the cable used?

I'll have to get up into the loft for this information. Haven't got time at the moment but hopefully will be able to later on.

Will be off-the-air for a while now.

Thanks.

 

[sm1thson]

Hmm, could you tell us the rating on the immersion heater?

-and confirm that there is only one heater!?!