Discuss Grid switches on 32A ring in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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might never exceed 20A through the switch but why do i keep finding them burnt out and occasionally bridged? spawn of the devil, would never fit myself.
They burn out because they’ve been installed badly, often by fitters of kitchens. And I agree, pain in the whotsit, and mostly pointless.
 
might never exceed 20A through the switch but why do i keep finding them burnt out and occasionally bridged? spawn of the devil, would never fit myself.
There's thousands out their with no problems. Perhaps those that have caused issues are like problems RFC's have, to the unanitiaive. (cant be arsed to spell it correctly)
 
Sorry all to revive an old post. I’ve often thought 20A switches are underrated so was looking for alternative. I’m installing a grid switch to feed appliances in the customers house. I’m using Scolmore Minigrid 32A switches, this allows full current through the RFC without worrying about terminals over heating. What are your views on this solution?
 
Don’t see the problem. A grid switch isolating a single appliance should never have to handle more than 13A. Unless you have a double socket, even then the expected load shouldn’t exceed 20A.


. I’m using Scolmore Minigrid 32A switches, this allows full current through the RFC
But you should never be interrupting the ring final. That’s the only place where the higher current might be found. Even then it’ll be around 20A max.
The switch will only ever see the current on the (switched) spur.
 
Incase I wasn’t clear the 32A switch allows the RFC to continue at a potential full load on the supply as the terminals are rated at 32A as a pose to 20A on many grid switches. Only one socket/appliance on the load side.
The switch is rated at 20 amps not the supply side terminals which are designed for much higher currents.
 
Looking at the specifications of MK 20A grid switches, they quote the input terminal capacity as 3 x 2.5mm or 2 x 4mm or 1 x 6mm. The MK 32A cooker switch has the same input terminal capacity figures. I don't see any MK specification for the maximum through current between two conductors stuffed in the same input terminal, but I suspect from the above is that it would be more that the rating of either of those switches.
 
Sorry all to revive an old post. I’ve often thought 20A switches are underrated so was looking for alternative. I’m installing a grid switch to feed appliances in the customers house. I’m using Scolmore Minigrid 32A switches, this allows full current through the RFC without worrying about terminals over heating. What are your views on this solution?
I suspect the terminals on any switch are probably not the limiting factor, it's the connections within the switch that may be. I see their 32A switches are double width, so the extra space may allow for meatier internals and a higher rating on the throughput. They also do a 20A DP switch of the same size though, so maybe it's mostly marketing. Would be interesting to take one of each apart and see what the difference is.

The terminals on all but the cheapest accessories could probably easily cope with 32A for straight in and out connections. Sockets are mostly rated at 20A after all but still are fine on a ring - whenever I've seen overheat damage it's usually due to loose connections, and it's the plastic that gives up not the terminal.

Having said that, I have started using the minigid light switches a lot recently, and they seem pretty well made so seems like a neat solution to provide isolation of under worktop appliances.
 
I thought a 20A DP switch was rated at 20A. Please point me in the directions of the specifications for a 20A DP switch where the input terminals are something else
TBH I could have worded my response a little better. The supply side terminals don't have to be load rated as such due to the fact they clamp conductors together and take no load themselves.
 
Ok, forget about diversity and unlikely loading conditions for the moment.

A grid switch assembly with 3 DP switches each supplying 3kW loads.

Now if the Grid switches are at the centre of the ring then we would expect 37.5A available when all the loads are active and for a DC supply 18.5A divided between the outer two switches supplying 12.5A to the middle switch but as its ac current the current flow across all of the input terminals would 37.5A, 25A, 12.5A every 10ms then the same in the opposite direction for a further 10ms continuing until the loads are switched off.

If the grid switch assemby is ofset in the ring then the current flow through the switches would be proportionally more on one side of the ring.

The input terminals are therefore loaded by the loads throughout the ring.
very important to make sure the terminals are tight.
 
clamp the line at the meter tails. I’ve had all my appliances on, drier, washer, dishwasher, never got over 20 amps, all be it, it was for around half an hour only, you’ll never see 30+ amps at all unless they are a resistive load like a water heater
 
A grid switch assembly with 3 DP switches each supplying 3kW loads.

Now if the Grid switches are at the centre of the ring then we would expect 37.5A available when all the loads are active and for a DC supply 18.5A divided between the outer two switches supplying 12.5A to the middle switch but as its ac current the current flow across all of the input terminals would 37.5A, 25A, 12.5A every 10ms then the same in the opposite direction for a further 10ms continuing until the loads are switched off.
I'm not sure that's right fella, unless there's something I'm missing?

Each DP switch would have its equipment's load of 12.5A flowing through it, both line and neutral.
The terminals of the switch dead centre of the ring would only have that 12.5A passing through them.
The one to the left would have it's load of 12.5A passing through its terminals, plus half of the centre switch's load as it passes by on its way to/from the consumer unit. So 12.5+6.25=18.75A. Exactly the same for the switch to the right.

The fact that it's AC is irrelevant.
 
Looking at the specifications of MK 20A grid switches, they quote the input terminal capacity as 3 x 2.5mm or 2 x 4mm or 1 x 6mm. The MK 32A cooker switch has the same input terminal capacity figures. I don't see any MK specification for the maximum through current between two conductors stuffed in the same input terminal, but I suspect from the above is that it would be more that the rating of either of those switches.
There’s not a chuffing chance you can get 2x4mm or 3x2.5 in a terminal on a 20A MK grid switch. There no where near a cooker switch size. Got to be a mistake in the literature there.

I said it in April 2019, they may be compliant, you need a 47mm deep back box, but every single one of these I have seen has been as rough as a badgers (thank you whoever pointed out a badgers arse is tougher than a bears arse recently) arse. More copper showing behind these things than the 1.5mm line in the Doncaster cable factory.
 
A 4 gang grid is specced on our new build sites ,47 mm double back box, Deta grid modules, no issue whatsoever in connecting them in a proper manner, in the 5 years I’ve been there, there’s never been a single issue that I know of regarding installing a grid system on a kitchen ring final.
That’s washer, dishwasher, fridge and hob ignite or a combination of cooker hood as sometimes a 2 gang grid is also fitted for the utility accessories (washer and drier)
 

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