80amp DP Isolator and a 100amp Main Switch do you need both!

[telectrix]

i think i agree with spin on this. the "origin" of the installation is " the position at which electrical energy is delivered to an electrical installation". to my mind that point is the DNO fuse, therefore the main switch is the closest point of isolation to the fuse.

 

[imago]

It's not something I'll get too concerned about, but I'm with spin on this. Even if you ignore the regs (what a nice thought!) a main switch would be the single switch which controls the largest amount of circuits after the head/meter. So it has to be the first isolation point after the head/meter.

When you consider that there can be up to 3 metres of cable between the isolator and the CU which the CU switch does not cover then the switch in the CU can only isolate the installation partially even if it is the largest part.

That said, from what I can see of paperwork relating to installations 90% is worthless or missing. That which does exist is rarely used or seen by anyone other than the spark who wrote it, and maybe another spark working on the system at a later date. So you could probably note the transformer up the road as the main switch and no one would say anything.

 

[Guitarist]

Two main switches, I suppose next they'll have two main earth terminals.

There often are 2 main earth terminals, 1 block and 1 in the CU. Thing is, we tend to designate 1 and use that for connections (although I often see both used). As long as it is stated on the paperwork which one is the main isolator, then we have a main isolator for our paperwork. Remember, this is only for our form, and as long as they both work and comply, then my personal belief is that the one which could be used by the customer is the most important one.
Anyway, I'm out of this now before you get too upset with me.

 

[telectrix]

LOL, as long as things are clearly documented. the BS no is the same for either SW, just the rating might be different.

 

[drew35]

So if the person who posted that he removes the main fuse for "safety", has the main fuse in his pocket whilst "on the bog", is happy to leave an exposed un-fused live terminal. Because someone might switch an isolator back on? (Which is supposed to be lock off with a sign in place)

Do these main fuses get any kind of seal put back at the end of these jobs? Or is it ok that anybody could pull it without the use of a tool, and then stick their finger on the fore mentioned un-fused live?

I can only guess that it must be much harder in some areas of the Country to dial a number and ask for the DNO to meet you their to remove the fuse and put an isolator in place. Or even before you arrive? Hard to imagine?

 

[Guitarist]

That's why "dummy" fuses are always used Drew

 

[rustynails]

So its a main switch rcd. What earthing system does the house have?

No, the new Main Switch inside the CU is not an RCD just a 2 Pole 100A main switch. The current isolator is a DP Wylex CAT WEM 80/2 100Ma Trip 80A Load 240v 50Hz, this has an RCD.

I had a similar situation a few weeks ago and checked with Elecsa, and the opinion was that either can be used on the form, just as long as it conforms with regs. Personally, I use the CU isolator

If this is true, then I too think I would prefer to use the new Main Switch as the primary supply overcurrent device.

If I did the isolator and I could not lock it off correctly it would be easy for someone to come past and turn the isolator on while I was on the bog.

This is true, I don't think I can lock off the current isolator off.

now what he does not mention is the size of the cut out fuse

The service head fuse is 60 amps.

The switch in the CU cannot be the main switch, if there is another switch between it and the origin of the installation.

This was also my take on the regulations too. Primary switch being the first piece of isolating equipment between the CU and service head.

:rolleyes2:

 

[Guitarist]

Remember rusty, a switch is not an overcurrent device.

 

[rustynails]

Remember rusty, a switch is not an overcurrent device.

That's true my mistake. The DNO fuse is the primary supply overcurrent protective device.

 

[oldtimer]

I dont know what the problem is here you have a 60A DNO fuse a Wylex 100mA RCD 80A rated switch that supplies a consumer unit that has a 100A rated switch inside it so what am I missing here ?

As I mentioned in a earlier post a 100A rated main CU switch is standard in but the DNO supply cna be 60A-80A or 100A either way the switch is fit for purpose I would be more concerned if there was a 100A DNO fuse and 10 way CU with a 60A rated main switch

 

[rustynails]

I dont know what the problem is here you have a 60A DNO fuse a Wylex 100mA RCD 80A rated switch that supplies a consumer unit that has a 100A rated switch inside it so what am I missing here

No problem, just wanted to see what people thought about having two pieces of isolating equipment between the CU and the Service Head. Personally, I think it's a little old school to have a further isolator outside the consumer unit. I'm all for keeping it neat and tidy within the consumer unit. Then all the end user has to understand is that if they have a power problem then all the on/off switches are in one place, easily accesible.

I was just waying up the advantages/disadvantages of keeping the old isolator in place. One of the disadvantages of removing it would be losing an 100ma RCD on the main switch. Without an RCD the main switch wont trip which I think is a bit annoying because in the new RCBO board the home owner would have to go along turning circuit after circuit back on, without an overall control. Not sure I rate that, seeing as thats what the owner had before, although RCBO's will be a significant step forward instead of the current rewirable situation.

One possibility would be to buy a different main switch with 100ma RCD, pull the fuse and get rid of the old wylex isolator allowing the owner to keep control over all the circuits in the event of a problem, although the RCBO's are very safe so I'm splitting hairs...

 

[Heisenberg]

Is it considered acceptable to have any sort of RCCB as a main switch? Surely even a 100mA one might allow for nuisance tripping :confused5: albeit not as much as a 30mA device.

 

[Guest55]

If theres a 100ma stand-alone rcd i'm instantly thinking TT unless i'm missing something ???
Has the OP confirmed supply earthing configuration ??
Lots of other basic errors being made in this thread sadly.

 

[telectrix]

the whole point of the up front isolator is to enable safe isolation of the CU without resorting to cutting seals.

 

[oldtimer]

this is getting silly so I am unsubscribing

 

[rustynails]

If theres a 100ma stand-alone rcd i'm instantly thinking TT unless i'm missing something ???
Has the OP confirmed supply earthing configuration ??
Lots of other basic errors being made in this thread sadly.

It is a TT with a high 386 Ohm ze reading as well...

 

[Guest55]

It is a TT with a high 386 Ohm ze reading as well...

This info may of been helpful at the beginning of the thread ??? :-/
Anyway if youre gonna fit a new dual rcd CU i'd be replacing the 100ma rcd with a DP switch.
And the rod Ra could do with improving as well.

 

[rustynails]

This info may of been helpful at the beginning of the thread ??? :-/

How's that then? The original post was about getting rid of an electricity isolator switch and replacing it with a main switch inside a new board.

Anyway if youre gonna fit a new dual rcd CU i'd be replacing the 100ma rcd with a DP switch.

The new board will have a dp 100A main switch and all circuits will be RCBO'd.

And the rod Ra could do with improving as well.

I'm going to have to fit another rod to try and bring that reading down hopefully.

 

[telectrix]

start by replacing the rod with screwed together 5/8" rods. go at least 3 ft. from the house wall to avoid bob the builders rubble.