working out volt drop

[shanky887614]

What has PME go to do with RCDs at both ends ?

he is a trainee mate with 8 posts.

to op ask your mentor what they would recommend but you shouldn't be designing it yet because there are errors already and you might make a hash of it.

before you do this answer a couple questions first.

ccc of 2.5 swa,twin etc
why do we use rcd's?
why is having two rcd's in series a bad idea?

in a TT system what is the difference between the upfront rcd and a 61008?

 

[spark 68]

Supply SWA connected in to switch fuse. RCD/RCBo's at the board!

Pointless having an RCD both ends unless the upstream one is S type. Not really necessary with PME?

Any thoughts on this anyone?

That is what I was getting at, the SWA does not need RCD protection on a TN system, two 30mA devices won't discriminate anyway, I was wondering why the OP brought PME into a (possible?) reason for the supply RCBO ?

 

[shanky887614]

That is what I was getting at, the SWA does not need RCD protection on a TN system, two 30mA devices won't discriminate anyway, I was wondering why the OP brought PME into a (possible?) reason for the supply RCBO ?

he is a trainee, i wouldnt be suprised if he is a first year

it sounds like a homework question, if it is its in the wrong section


he mentions mv/a/m on basic domestic circuits so its homework, why would you need to work this out when it gives you all that info in bs7671 and onsite guide if we wanted it

 

[Simonslimline]

he is a trainee, i wouldnt be suprised if he is a first year

it sounds like a homework question, if it is its in the wrong section

His profile states 17th and part P. I wonder what course he is actually doing?

 

[shanky887614]

His profile states 17th and part P. I wonder what course he is actually doing?

must be a Electrical Trainee with that kind of question

 

[spark 68]

I wasn't having a go at him Shanky , just curious as the thinking behind it that was all , I must admit that I had dark thoughts of someone thinking a source/supply RCD may somehow negate possible bonding issues with PME, as I have heard this before from someone who should have known better

 

[baldsparkies]

which is less then the max of 6.9v or 3%

3% of supply voltage 7.2v :sorcerer:

Europe friendly lick the bottom value 6.9v :dunce2:

 

[Darkwood]

It's suppled from a pme system
rcbo at supply end and rcd at garage end but over the top but it's not going to give any nuss tripping.
4mm fro radial (got in in the van )

Over the top is one one thing but wasting money and having no discrimination of 2 rcd in series thus does not comply to regs is another, yes its not going to give nuisance tripping par' ce but its poor design from a professional all the same.

 

[baldsparkies]

Am I missing something ??
So tripping the Rcd on the test button wont take out the Rcbo ?????

 

[Lucien Nunes]

No, it won't. Or am I missing some of what you missed?

 

[spark 68]

No, it won't. Or am I missing some of what you missed?

Of course it will also trip the upstream RCBO Lucien, have a think for a moment how the test button works.

 

[Lucien Nunes]

I have thought for a moment and I cannot see why an ordinary RCD test button would trip an upstream RCBO. Pray tell...

 

[telectrix]

just out of interest, can anyone quote a reg. that forbids 2 30mA RCDs in series?

 

[Silly Sausage]

just out of interest, can anyone quote a reg. that forbids 2 30mA RCDs in series?

Reg 1: Use Common sense.

or it'll be something out of Chapter 3 about discrimination.

 

[spark 68]

I have thought for a moment and I cannot see why an ordinary RCD test button would trip an upstream RCBO. Pray tell...

Right, I have had a thought , and it seems maybe you are correct and I was wrong for this scenario being that the RCBO is upstream and the RCD is downstream, however if the RCBO and RCD were the other way around then it trips both devices for some reason, maybe something to do with the functional earth on the RCBO ?

I know this as a fact because I once was testing a custom built SP DB (by the firm I as working for), and all of the test rigs were in use so I used a normal socket outlet and "widow maker" lead to power this DB up to check the metering etc., anyhow I accidently caught one of the test buttons on one the many RCBOs fitted to this board and promptly tripped out the supply RCBO for this supply too, the howls of protest from a co-worker whom was using a computer powered from this supply revealed this lol