Choosing a power supply, switch fuse size

[Yanu]

Hi all, I'm new here.
I have qualified back in 1990 and worked only a few years in the trade. Now I'm back and I find myself a bit "rusty" and in need of a bit of help...

I have to wire a complex of coldstores and I have to make a fuse boards for a part of them. I have 6no 10 amp MCBs, 2no 20 amp MCBs and 8no 20 amp RCBOs in it. Just a few lights and sockets circuits. I have no idea what's going to be plugged in and for how long, the client can supply single or three phase.
What size switch fuse do you think I should use?
Thanks in advance

 

[Dillb]

Do you think my guess on the breakers is not right?

Seriously?

 

[Yanu]

So are you going with the 'maximum rating' or 20A??


Either a Ring Main (it's Friday and that's going to annoy quite a few people) or a Radial.

Yes spoon, they are wired with 2.5 pvc single and I always thought that would be the maximum rating, do you think I'm wrong?
I have wired those rooms with two feeds. The plan is to have two circuits with 4 socket or a ring of 8

Thanks

 

[Yanu]

So are you going with the 'maximum rating' or 20A??

Yes spoon, they are wired with 2.5 pvc single and I always thought that would be the maximum rating, do you think I'm wrong?

Either a Ring Main (it's Friday and that's going to annoy quite a few people) or a Radial.

I have wired those rooms with two feeds. The plan is to have two circuits with 4 socket or a ring of 8

Thanks

 

[Yanu]

Seriously?

Yes Dillb, I'm quite serious.... Did I write something completely stupid?

 

[westward10]

You cannot be guessing the circuit design and then ask people on a forum who have no knowledge of the site to confirm your guesses are correct.

 

[Spoon]

Yes spoon, they are wired with 2.5 pvc single and I always thought that would be the maximum rating, do you think I'm wrong?

I think you are wrong in that you are designing a circuit based on what cable you have.....
You say you want the max rating. Well then use the appropriate wire for that rating. Simple.

 

[Spoon]

I have wired those rooms with two feeds. The plan is to have two circuits with 4 socket or a ring of 8

Thanks

Sorry mate... I'm confused. Why use a different wiring method for 4 or 8 sockets? What is the reason?

 

[Yanu]

I think you are wrong in that you are designing a circuit based on what cable you have.....
You say you want the max rating. Well then use the appropriate wire for that rating. Simple.

Sorry Spoon.. how would you wire a socket circuit? wouldnt you use a 2.5 cable for it. Wouldnt you put a 20 amp rcbo for that?

 

[Yanu]

Sorry mate... I'm confused. Why use a different wiring method for 4 or 8 sockets? What is the reason?

I remember an engeneer once told me to put a max of 4 sockets on a circuit and I'm following that advice. What's the max you'd put?

 

[Yanu]

You cannot be guessing the circuit design and then ask people on a forum who have no knowledge of the site to confirm your guesses are correct.

I have no knowledge of the site either. I have to do a job and looking for help, this seemed the right place for it. I seem to be getting lots of hassle here on how little I know and nobody is really telling me what they would do in my position

 

[MJPD29]

Hand dryers will require rcd protection for a start, there is not a limit of 4 sockets either, but if you don't think your capable of doing the job (that's not a jab at you by the way) id say to your boss that you don't think your able to, you probably shouldn't undertake it if you can't provide the correct protection for each circuit. Will you be able to test it when finished?

 

[westward10]

You said previously these cold stores are normally straight forward, what is different now. If you have no knowledge of the site then that should be your first port of call, either visit the site or see specifications for the site.

 

[telectrix]

I remember an engeneer once told me to put a max of 4 sockets on a circuit and I'm following that advice. What's the max you'd put?

well he told you a load of cobblers. you need to stop guessing and calclulate properly. first determine the design current Ib. then select your cable so that it's max. current Iz > Ib. then select OCPD according to Iz>In>Ib.where In is the OCPD rating in amps. then calculate VD to ensure that the cable you have selected is suitable.

 

[Risteard]

Your location states Ireland. Am I correct in assuming that these jobs are in the 26-Counties?

 

[Yanu]

Your location states Ireland. Am I correct in assuming that these jobs are in the 26-Counties?

Yes, they will be shipped to Scotland