Outside BAR

[Hager]

HI

I've looked in too this before but never go round to it. I have a quick Q on the electrics.

The pic i have attached is how i was going to do it.
The max load i have is 20A- So it might just be enough for what i want to run.

Should i have Two small radials as in the pic for should it just be 1 hole radial? the loads on the sockets will be quite small, things like chargers (laptop and ipods etc etc) and an amplifier will be used, along with 2 fridges the plan was two put one on each radial so if the MCB trips on say radial 1 he drinks will still be cold on radial 2.


The other thing is the lighting load will be approx 3KW +20% if we decide to flash them.

Untitled

• Hager
• 25 Apr 2011
• 1

EDIT- I plan to use 8X PAR 16 nows and they are only 50W GU10 bulbs per can, i forgot to mention there will also be a 1.3KW Patio heater + 2x 360W tube storage heaters for the winter.

 

[electronicsuk]

It may be better to run a submain in SWA to a small weatherproof DB at the bar containing RCBOs. The submain can be fed from a non-RCD way in the house, or via Henleys and a switchfuse if that's more appropriate.

These issues aside, your asking of such basic questions makes me wonder if you really should be carrying out this work at all. I assume you'll be notifying it to your LABC, who will ensure compliance with the building regulations?

 

[Hager]

HI

I never though of that. It might be an idea. It would have to be Henleys we have run out of ways in our CU. .

The question was really two radials or one, suppose that is quite basic. I have good knowledge to do this correctly though.

LABC will being notified after the bulid has been complete.
Could you give me an idea of what they would be looking for?
IF this helps it was going to be going to be done using 20mm Conduct and metalcald or IP55 sockets to be used. The bar will be under a gazebo style canopy. so IP rated sockets may not be necessarie unless you thing other.

Thanks
Jake

 

[rebuke]

LABC will being notified after the bulid has been complete.

That's not the way it works - you have to notify them *before* doing the work, otherwise there is a risk they won't approve the work and require you to rip it all out, and also even if they do approve it they are likely to charge you a higher regularisation fee compared to the normal notification ones...

 

[Hager]

Hi

That's not the way it works - you have to notify them *before* doing the work, otherwise there is a risk they won't approve the work and require you to rip it all out, and also even if they do approve it they are likely to charge you a higher regularisation fee compared to the normal notification ones...

When i said that i ment after the structure has been built and then ready for the electrics to be fitted, or was i supposed to notify them before i started to bulid the structure?

Thanks
Jake

 

[electronicsuk]

When i said that i ment after the structure has been built and then ready for the electrics to be fitted, or was i supposed to notify them before i started to bulid the structure?

Thanks
Jake

If the structure doesn't require BC notification then you only need to notify the LABC before the electrical work starts, unless there are other controlled services such as foul water drainage that may be required. However, surely the building and electrical works will go hand in hand, rather than being entirely separate processes?

WRT the radial circuits, you will obviously be better off with two in terms of redundancy. Personally, as you're starting from scratch, I'd install one radial circuit for each fridge, and then another for general use sockets.

 

[Hager]

HI

If the structure doesn't require BC notification

Arrrr, good. (But then the build has't quite started yet.)

notify the LABC before the electrical work starts, unless there are other controlled services such as foul water drainage that may be required.

That will be a while yet, so i can plan it out by the letter.
Nope its just electric we want.

However, surely the building and electrical works will go hand in hand, rather than being entirely separate processes?

I thought it might make it a bit eaiser, to make each bit one whole process.

WRT the radial circuits, you will obviously be better off with two in terms of redundancy. Personally, as you're starting from scratch, I'd install one radial circuit for each fridge, and then another for general use sockets.

I did think that but i thought it might be over kill on the CU. Don't really want to make it OTT.

Thanks
Jake

 

[ban-all-sheds]

Why 10A radials?

What on earth is the point of such small ratings, and what will you do if (as is quite possible) the start-up surges on the compressors are enough to trip 10A breakers?

Have you checked that the charges your LABC impose make DIYing a sensible idea?

What do you plan to do about testing?

When you apply for Building Regulations approval what will you say will be the way you'll ensure compliance with P1?

 

[JohnW2]

Why 10A radials?
What on earth is the point of such small ratings, and what will you do if (as is quite possible) the start-up surges on the compressors are enough to trip 10A breakers?

Indeed, that's a (I would imagine slight) possibility - but have some posts been deleted without my seeing them? Apart from you, I've seen no-one mentioning '10A radials' or '10A breakers'. What have I missed?

Kind Regards, John.

 

[Lectrician]

but have some posts been deleted without my seeing them? Apart from you, I've seen no-one mentioning '10A radials' or '10A breakers'. What have I missed?

See OP's pic

 

[JohnW2]

but have some posts been deleted without my seeing them? Apart from you, I've seen no-one mentioning '10A radials' or '10A breakers'. What have I missed?

See OP's pic

Ah! My sincere apologies to BAS; I totally missed that - I read all the prose carefully before writing my last post, but didn't read the piccie carefully enough!

I suppose I can understand how this arose. Separate circuits for the two fridges obviously means that both are not lost as a result of one MCB operating (which one could argue was called for by 314.1) but, even with 10A circuits, this takes the total load to 36A (10+10+16) - only just within the capabilities of 4mm² SWA, and way beyond 2.5mm² SWA (the pic says "2.5mm² or 4mm² SWA"). I doubt whether the intention was to wire the radials with anything smaller than 2.5mm², so I doubt that is the limiting factor.

If one wanted to stick with two radials (for 'division into circuits'), then I guess the better approach would be to use larger SWA (probably 10mm² - maybe squeeze through with 6mm²) and have 16A or 20A radials. I certainly would not think that 10A radials would be a good idea. I somehow doubt that the theoretical possibility (mentioned by BAS) of the start-up current of a fridge compressor operating a 10A MCB would be a significant risk in practice, but I would say that it's probably bad design to ever have only 10A protection for a circuit which has several 13A socket outlets. Using larger SWA would obvioulsy also facilitate a 32A ring, but that would not provide any 'division' (if one felt the need for it).

Kind Regards, John.

 

[Hager]

HI

I have been talking a decide to get a proper sparky to do the work.

I suppose I can understand how this arose. Separate circuits for the two fridges obviously means that both are not lost as a result of one MCB operating (which one could argue was called for by 314.1) but, even with 10A circuits, this takes the total load to 36A (10+10+16) -

I did lower the rating of the lighting so it will no longer be a 16A trip it will be a 6A decided to not bother with the other PAR cans so the 6A will only be supplying the PAR 16s total lighting load now 400W. (Sorry if this is a bit confusing)

only just within the capabilities of 4mm² SWA, and way beyond 2.5mm² SWA (the pic says "2.5mm² or 4mm² SWA"). I doubt whether the intention was to wire the radials with anything smaller than 2.5mm², so I doubt that is the limiting factor.

The problem is i only have 20A to play with, decided not to pull and extra supply from the CU it will just cost more and will mean a lot of concrete to be dug up. Don't really want big, thick SWA to be seen.

Yes the radials were going to be done with 2.5mm2 T&E in conduct.

If one wanted to stick with two radials (for 'division into circuits'), then I guess the better approach would be to use larger SWA (probably 10mm² - maybe squeeze through with 6mm²) and have 16A or 20A radials. I certainly would not think that 10A radials would be a good idea.

Would a fridge eat 13A in surges? If it does i might have to go the bigger thicker cable route. 10mm i guess if i do. The more power would help.


Could i get away with the two on a 20A circuit? these are the small under counter ones.

Thanks
Jake

 

[ban-all-sheds]

Don't really want big, thick SWA to be seen.

So is the SWA you were talking about already installed, and it's either 2.5mm² or 4mm² - you're not sure?

Or do you plan to have it installed, and you want to use only 2.5mm² or 4mm² because you don't want big, thick cable to be seen?

It's customary to design circuits on the basis if what they have to do, not on trying to keep the cables thin...

6mm² is barely larger than 4mm²...

Yes the radials were going to be done with 2.5mm2 T&E in conduct.

But they were only going to be 10A.

And if you're using conduit, don't use T/E.

10mm i guess if i do. The more power would help.

Even 10mm² is only about 4mm bigger in diameter than 4mm², but do you need that much capacity?

Could you draw enough from the shed CU to justify 10mm²?

Best to let your electrician start with a clean sheet...

 

[JohnW2]

I did lower the rating of the lighting so it will no longer be a 16A trip it will be a 6A decided to not bother with the other PAR cans so the 6A will only be supplying the PAR 16s total lighting load now 400W. (Sorry if this is a bit confusing)

OK, so as I understand it, you now want a 6A lighting circuit, plus the power; is that right?

The problem is i only have 20A to play with, decided not to pull and extra supply from the CU it will just cost more and will mean a lot of concrete to be dug up. Don't really want big, thick SWA to be seen...Yes the radials were going to be done with 2.5mm2 T&E in conduct....

I'm not totally clear as to what is this 20A that you 'have to play with', or what concrete digging you want to avoid. Are you now saying that you don't intend to bury the SWA?

2.5mm² SWA would take 29A buried and about the same not buried. That would allow you your 6A of lighting plus two 10A radials or one 20A radial, but the total would obviously then be 26A (more than your '20A'). The lighting plus one 16A radial would only, at 22A, be only just over your 20A (per MCB ratings) - but it sounds as if your lighting will now actually be well below 6A demand in practice, so the total actual demand would undoubtedly be well under 20A.

Would a fridge eat 13A in surges? If it does i might have to go the bigger thicker cable route. 10mm i guess if i do. The more power would help.
Could i get away with the two on a 20A circuit? these are the small under counter ones.

As I said before, I frankly very much doubt that a fridge compressor start-up would trip a 10A MCB, and I honestly doubt that even two would (if they happened to start simultaneously), either. I would therefore personally think that to have both fridges on one 16A or 20A radial (either of which could be wired in 2.5mm² T&E) would be fine - although it obviously would mean that if the MCB did ever trip, you'd lose both of them.

From what you said initially, it doesn't sound as if you want/need much other power, so I would personally think that a single 16A or 20A radial for everything (both fridges, plus the rest) would probably be fine.

I should have prefaced all this by pointing out that I'm not a professional electrician, so I add that as a 'postface' instead

Kind Regards, John.

 

[Hager]

HI

So is the SWA you were talking about already installed, and it's either 2.5mm² or 4mm² - you're not sure?

No, it's not installed yet.

Or do you plan to have it installed, and you want to use only 2.5mm² or 4mm² because you don't want big, thick cable to be seen?

Yes correct.

It's customary to design circuits on the basis if what they have to do, not on trying to keep the cables thin...

You are correct here sir.

But they were only going to be 10A.

And if you're using conduit, don't use T/E.

They where but i'm now thinking differently, if the fridges eat more than i thought they did.

Would you suggest singles??
I have noticed that is standard.

Even 10mm² is only about 4mm bigger in diameter than 4mm², but do you need that much capacity?

Could you draw enough from the shed CU to justify 10mm²?

Best to let your electrician start with a clean sheet...

I dont really need the capacity of 10mm for this (this is final on what i'm having)

2X fridges
2x tubular storage heaters
8X 50W Light fitting
and a amplifier.

OK, so as I understand it, you now want a 6A lighting circuit, plus the power; is that right?

Yes correct.

I'm not totally clear as to what is this 20A that you 'have to play with', or what concrete digging you want to avoid. Are you now saying that you don't intend to bury the SWA?

Sorry, The 20A is from the shed, the concrete digging i was trying to avoid is from the main CU (in the house) the bar will be build on the back of the shed so it's soil and it will have a PLY floor so the SWA can be put buried under that.

2.5mm² SWA would take 29A buried and about the same not buried. That would allow you your 6A of lighting plus two 10A radials or one 20A radial, but the total would obviously then be 26A (more than your '20A'). The lighting plus one 16A radial would only, at 22A, be only just over your 20A (per MCB ratings) - but it sounds as if your lighting will now actually be well below 6A demand in practice, so the total actual demand would undoubtedly be well under 20A.

The SWA will be buried for about 2-3m long and then brought in between the shed and fence and then under the slats that hold the shed up and then though a hole in the floor the it's CU.

The lighting is 1.66 amps. Arrrr good, under 20A would be very helpful.

As I said before, I frankly very much doubt that a fridge compressor start-up would trip a 10A MCB, and I honestly doubt that even two would (if they happened to start simultaneously), either. I would therefore personally think that to have both fridges on one 16A or 20A radial (either of which could be wired in 2.5mm² T&E) would be fine - although it obviously would mean that if the MCB did ever trip, you'd lose both of them.

I did think that they are only fitted with 1mm flex if i remember rightly.
Suppose it would only be quite rare for one to trip, unless there a fault of course.

From what you said initially, it doesn't sound as if you want/need much other power, so I would personally think that a single 16A or 20A radial for everything (both fridges, plus the rest) would probably be fine.

I should have prefaced all this by pointing out that I'm not a professional electrician, so I add that as a 'postface' instead

A single radial would be easier, but then that's for the sparky to decide. he will probably thing the same.

Thanks
Jake