RCD Waterproof socket

[SparkJ]

Hi All

I have been asked to quote for a replacement 17th Edition consumer unit for an old house. The earth system is TT and the current CU is the semi enclosed wired fuse type.

On the outside of the house there is an existing MK twin waterproof socket with built in RCDs connected to the downstairs ring.

The customer wants to retain this as they were expensive.

Is there an issue of discrimination with having an RCD protected consumer unit and RCD incorporated in a socket as well?

I know that having an RCD in a ring main messes up the insulation resistance readings of the circuit big time but I was wondering if it screws up other things also.

 

[green-hornet]

Both the socket and the rcd in the cu will be 30mA so there could be a difference in the time they disconnect but that is down to the sensitivity of the rcd's.

A ramp test could show which one will trip first I would suspect it would be the house or cu rcd as this is warm and dry and may be tested more frequently.

Take the socket off for any insulation testing.

I would not worry too much about the discrimination but explain to the customer the chances are that the house rcd may trip first.

 

[grandad]

as the hornet said.also if you change the socket for non rcd and a fault develops.the main rcd will trip anyway,so you will end up with the same result.by keeping the rcd socket there is always a chance that it will be the only one to trip,but unlikely.

tell the customer you have worked it so he/she can keep the rcd socket,and they will think you are terrific

Blushing

 

[Andy™]

RCD's do have a high failure rate. so the more the better. hopefully, if there is a fault and one fails, the other wont

 

[Andy™]

Both the socket and the rcd in the cu will be 30mA so there could be a difference in the time they disconnect but that is down to the sensitivity of the rcd's.A ramp test could show which one will trip first I would suspect it would be the house or cu rcd as this is warm and dry and may be tested more frequently.

Take the socket off for any insulation testing.

I would not worry too much about the discrimination but explain to the customer the chances are that the house rcd may trip first.

have to disagree there - how many people actually test the RCD in the CU.... where as socket RCD is right in front of you when plugging in extension/lawnmower, and so could be tested more.

 

[Apache]

tell the customer you have worked it so he/she can keep the rcd socket,and they will think you are terrific

It's not what you do - it's how you do it. A VERY important point there

 

[green-hornet]

have to disagree there - how many people actually test the RCD in the CU.... where as socket RCD is right in front of you when plugging in extension/lawnmower, and so could be tested more.

You are correct and I could not disagree with you, that is why I stress to my customers the importance of doing the test and give them a step by step guide on how to do it, just because we know and fully understand the process does not mean that they do. Its all down to educating your customers and letting know its there., and how to do the simple tests.

 

[Blue Fox]

have to disagree there - how many people actually test the RCD in the CU.... where as socket RCD is right in front of you when plugging in extension/lawnmower, and so could be tested more.

I have to agree with andyc, I know a couple who have the plug in type RCD that goes into the socket then you plug into that for the lawn mower and they test it everytime they go to use it. Bet if I fitted an RCD in the consumer unit they wouldn't test it every day before they turned anything on!!

 

[Andy™]

You are correct and I could not disagree with you, that is why I stress to my customers the importance of doing the test and give them a step by step guide on how to do it, just because we know and fully understand the process does not mean that they do. Its all down to educating your customers and letting know its there., and how to do the simple tests.

you can explain all you like. after the first 3 month it may be tested, but thats probably it, and only tested from there if there is a fault

but this also makes you think of who's house is safer

Mr A has loads of dodgy gear, which keep randomly tripping RCD. one day he gets a shock and RCD is well tested, and so trips quickly, saving him

Mr B has loads of well looked after equipment, but never tests RCD. one day he gets a shock and RCD fails, killing him

 

[Badger]

does it count that i do regular checks on our rcds

 

[Andy™]

does it count that i do regular checks on our rcds

i should know better... but only time RCD in my house gets checked is when i need to turn the power off for something or if there is a fault

 

[green-hornet]

This is the last report that the ESC did on the subject of RCD,s

as you can see from the report 96% appeared to be "fault free" but the emphasis has always been put on the fact that the regular testing must be carried out.

http://www.esc.org.uk/news-and-events/research/industry/rcd/january-08.html

 

[Apache]

does it count that i do regular checks on our rcds

I check mine every couple of months