Discuss 80amp DP Isolator and a 100amp Main Switch do you need both! in the Electrical Forum area at ElectriciansForums.net

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I've seen various posts about this but wanted to start a new one, nothing like repitition. I am installing a new CU and it currently has an 80amp DP isolator between the service head and two split old wylex rewirable boards. I will be installing a 14 way board which comes with an 100amp Main Switch and every circuit will be protected by an RCBO. Seeing as it's illegal to tamper with the service fuse... I guess it is advisable to leave the DP isolator in place, it just seems unecessary.

Anyone have any thoughts on this...
 
S

stuart569

Is it an Mccb or a switch fuse? The chances of it ever blowing are slim to none so really isnt doing any harm and is very handy for board changes etc ... like your doing
 

telectrix

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Mentor
Arms
Esteemed
as above. useful to isolate CU without cutting seals.
 
D

Deleted member 26818

Just remember, that the DP isolator will be your main switch on the paperwork.
 
P

paddyscouse

i wouldent trust the dp isoater, on any instalation i rarther be safe and pull the fuse
 
  • Thread Starter Thread Starter
  • #9
Is it an Mccb or a switch fuse?
The current DP isolator is a Wylex CAT WEM 80/2 100Ma Trip 80A Load 240v 50Hz. The new board is a QFS-X16M with a 100A Main Switch (two way) so that would shut off the neutral and the live conductors.

telectrix said:
useful to isolate CU without cutting seals.
Yep that's part of the argument for keeping it in, any future changes to the board could be isolated from the seperate DP isolator.

spinlondon said:
Just remember, that the DP isolator will be your main switch on the paperwork.
Good point, thanks.
 
Just remember, that the DP isolator will be your main switch on the paperwork.
The DP isolator does not have to become your main switch on paperwork if there is one inside the CU. 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, as this is the one the customer has access to in every case.
 
S

stuart569

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

SKY

I too would pull the fuse and keep it in my pocket until I have finished the work.
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.

OK I work mainly on commercial properties where there is a chance of someone doing the above so always try to isolate in a fail safe way.
 
D

Deleted member 26818

The DP isolator does not have to become your main switch on paperwork if there is one inside the CU. 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, as this is the one the customer has access to in every case.
I think ELECSA need to re-read the Regulations.
Specifically: 537.1.4 "A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation.....".
 
O

oldtimer

I may be picking this up wrong but the op is concerned that he has a 80A switch feeding a 100A switch in a CU now what he does not mention is the size of the cut out fuse. So here is my tuppance worth dont pull the fuse switch off the 80A isolator test to confirm that the outgoing cables are dead then disconnect them and now you are good to go . Fit the new CU do your tests get your tails ready and again test the 80A isolator then connect your tails ensuring you have the CU main switch off then once you are happy switch on the 80A isolator and go through the proving sequance at the CU main switch and because you have done all your tests do a final check on ALL of the CUs connections and now you can switch it on

Or am I missing something


I forgot to add this happens all the time in flats that have 60/80A fuses but when you fit a new CU or any CU they always have a 100A rated main switch plus thats the last thing to worry about as people are fitting 11kw showers in flats
 
I think ELECSA need to re-read the Regulations.
Specifically: 537.1.4 "A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation.....".
I don't see how this excludes the use of the DP isolator at the CU as suitable for being used on forms tho spin.
 
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