Spark from immersion heater switch

[Harry Bloomfield]

Yes, 20a, DP. New one is from wickes for £3.x. The old one, I can't quite make out the brand.

A cheapy then. Better ones will have a snappier action and more robust contacts, both will help reduce arcing.

 

[DiyNutJob]

When it is turned on and you feel the switch, does it feel warm?

OK, that's what I will look out for in the future. It's just the sparks scaring the family members. I have just replaced the central heating pump. There should be no more need for the immersion heater now.

 

[DiyNutJob]

A cheapy then.

Says 5 year guarantee. I will go see them when it melts.

 

[Colin Brenton]

See if you can fit a 40 or 50 amp rated (cooker type?) switch into the box. It will be loaded at less than half of its capacity, rather than around three quarters, and will have heavier duty contacts etc.

Something like this might be suitable? https://www.cef.co.uk/catalogue/products/4330404-50a-dp-1-gang-switch-white

 

[EFLImpudence]

The sparking when switched off only happens when someone is looking at the switch; if no one is looking it doesn't spark.

Either way, it doesn't matter.

 

[Colin Brenton]

Haha, true. Time your blink reflex carefully

 

[SUNRAY]

Hi,

This may be slightly over the top, but could it be worth considering a 2-pole isolator?
Something like this:

View attachment 252053

https://www.sparkswarehouse.com/col...ducts/bg-cprsd220-rotary-isolator-2p-20a-ip65

They are significantly 'beefier' than a standard switch, and easy to turn on and off.

Edit: although it wouldn't be a straight swap, cable glands and a fused outlet would have to be considered.

The problem is, when arcing occurs, the switch contacts are damaged. This causes higher resistance within the contacts, eventually causing even more heat damage.
A destructive feedback cycle!

...and yes, it is possible that there is something wrong with the immersion!

But that isolator will also arc if switched of under load.

 

[RandomGrinch]

But that isolator will also arc if switched of under load.

Yep, most will.
Unless intrinsically safe, and even then, only when designed as part of an IS system.

However, I would bet that the isolator would last a good deal longer than a cheap switch from Wickes!

...and you would definitely not see the sparks in there

I may be wrong, but there seems to be a more positive 'break' in the contacts (and a greater travel distance), when turning a rotary isolator, compared to flipping a switch.

Though as @Colin Brenton suggests, the 40A cooker switch would fit nicely without additional work, could cope better with the switching current and would look better if the switch was visible. I assumed, maybe wrongly, that the switch was in a cupboard!

 

[Harry Bloomfield]

However, I would bet that the isolator would last a good deal longer than a cheap switch from Wickes!

...and you would definitely not see the sparks in there

I may be wrong, but there seems to be a more positive 'break' in the contacts (and a greater travel distance), when turning a rotary isolator, compared to flipping a switch.

Yep - The contact is broken by a very positive spring action. They are not dependent on the operator flicking the switch, the operator winds up a spring, then the spring reaches a point where the spring flicks the contacts suddenly open. The are much better at dealing with inductive loads, such as motors, where there is even more tendency to arc, than a resistive load.

 

[DiyNutJob]

See if you can fit a 40 or 50 amp rated (cooker type?) switch into the box. It will be loaded at less than half of its capacity, rather than around three quarters, and will have heavier duty contacts etc.

Do you know that works for a fact, or are you merely speculating?

From what I understand about the sparking issue is that the cause is the amount of energy present. Having a bigger or bigger-capacity switch does not reduce the energy present. The same size spark will be produced by the same energy. The only thing that would make a difference would be the contact material. Maybe some materials are better able to prevent arcing.

Also, are you sure there are no regulations that says you are not allowed to confuse electricians who might be working on that switch?

 

[SUNRAY]

Larger switches are obviously designed to cope with switching heavier loads, if we go to extremes (say a 1000A switch) the effect of a 13A load will be greatly reduced as the contact will open wider and quicker.

Would it be more confusing if this has a cable going to an immersion heater:

as opposed to this:

 

[RandomGrinch]

...and as we have said regarding isolators;
Have you tried flicking the switch of a cooker switch?
The action normally requires more force and is far more positive, than with a standard switch.

 

[DiyNutJob]

...and as we have said regarding isolators;
Have you tried flicking the switch of a cooker switch?
The action normally requires more force and is far more positive, than with a standard switch.

Yes, I have tried flicking the cooker switch. It is not connected. However, the 13A socket switch on it sparks.

 

[DiyNutJob]

Larger switches are obviously designed to cope with switching heavier loads

The spark size and strength is caused by the energy present. Bigger or smaller switch doesn't change the energy present. No matter how fast you flick the switch, the arc operates at the speed of light. As soon as the switch breaks contact, the arc charge begins.

 

[Harry Bloomfield]

Do you know that works for a fact, or are you merely speculating?

From what I understand about the sparking issue is that the cause is the amount of energy present. Having a bigger or bigger-capacity switch does not reduce the energy present. The same size spark will be produced by the same energy. The only thing that would make a difference would be the contact material. Maybe some materials are better able to prevent arcing.

Also, are you sure there are no regulations that says you are not allowed to confuse electricians who might be working on that switch?

There are no such regulations preventing the installation of a more robust than strictly necessary switch. The action of the switch will be brisker, the contacts more capable, therefore the resultant arc will be shorter and less obvious. Arc duration is a function of the speed with which contact is broken, which is why higher current and voltage switches, use a wind up and press a mechanical button to trigger make or break and/or oil submersion and/or an insulated barrier dropping into the gap to break the arc.