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]

How can you design the panel if you have no idea what they are going to plug into it? You need to ask the client for more information.

 

[loplug]

300mm x450 mm nice bit of room to work in then. Haven’t a clue on the correct rating of the fuse tho would need more info for that

 

[Pete999]

Where is my wand? I had one cuz I made it myself

 

[Wes1000]

If you don’t know what’s being connected or for how long the loads are on the circuits you won’t be able to apply any diversity to the load. You need to speak to the client as others have said.
Who decided on the protective devices and their ratings, how was this decided on? Surely you must have had some design spec.

 

[davesparks]

Why do you need a switchfuse?

 

[westward10]

Sounds like this task is well outside your remit.

 

[Octopus]

Where is my wand? I had one cuz I made it myself

Your wand is with my crystal ball..........................

lord knows what the heck this is all about

 

[Risteard]

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

Are you registered with RECI?

 

[Yanu]

Thanks for your comments guys, I have more information this morning.

I'm not registered with RECI, I'm employed by a company that builds coldstores and they only require my qualification to sign them off.

There are a total of 25 lights, 5 foot LEDs, they are only 63 w each. I'd like a separate MCB for every room. 6 rooms, 6no 6amp MCBs?

My employer says that the sockets are for general use and to go with the maximum rating to cover ourselves. There are from 4 to 8 in each room. 6 circuits, 6no 20 amp RCBOs? I might wire the ones with 8 sockets as a ring.

There are 2 spurs for hand driers, 2no 20 amp MCBs?

2no panasonic air conditioners, 2no 20 amp RCBOs or MCBs, not sure

Back in the days I use to wire the mains to a switchfuse in the consumer units, is that not the case anymore?

Thanks

 

[Scotty R]

You really shouldn't be undertaking the work if you're not confident in your own knowledge and competence because if something goes wrong you're responsible and you will have to justify everything and every decision you've made from the design, installation and testing. Asking here gives you no cover should YOU cock something up.

 

[Yanu]

You really shouldn't be undertaking the work if you're not confident in your own knowledge and competence because if something goes wrong you're responsible and you will have to justify everything and every decision you've made from the design, installation and testing. Asking here gives you no cover should YOU cock something up.

I'm sure there are times when you are not sure about things right?
Usually these coldstores are straight forward to wire and I have no problem with them. Sometimes we get the odd job and I can't say to my boss that I'm not doing it...
Do you think my guess on the breakers is not right?

 

[Scotty R]

If I'm unsure of anything I refer back to the relevant legislation I don't go on forums with a vague outline of proposed works to seek confirmation. You should have all the correct design and cable calcs for the installation and that should provide you with all the info you need. If you don't.....Well what are you playing at

 

[Yanu]

If I'm unsure of anything I refer back to the relevant legislation I don't go on forums with a vague outline of proposed works to seek confirmation. You should have all the correct design and cable calcs for the installation and that should provide you with all the info you need. If you don't.....Well what are you playing at

I have no choice and I have to do the job.
Unfortunately I don't know as much as you about the trade but it is what it is... I can't change that.

I don't think my choice of breakers is far from what it should be, you still haven't express an opinion about that.
If you have no intention of helping, you don't have to keep replying otherwise we will be both wasting our time to get anywhere.

Thanks for your comments so far

 

[Spoon]

My employer says that the sockets are for general use and to go with the maximum rating to cover ourselves. There are from 4 to 8 in each room. 6 circuits, 6no 20 amp RCBOs?

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

I might wire the ones with 8 sockets as a ring

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

 

[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