New Garage CU

[Onoff]

Been and had a measure. Existing cable is 4 core, 4mm SWA (red, yellow, blue, black). Length immaterial as it's going.

Sketch just for my benefit. 25m from new cu position to garage cu then 6m from there to the EV charger.

Quickly through something in CAD, crap resolution:

Later more thinking, now it's pub o'clock so...

 

[Onoff]

I've got planned 16 mm T&E to the garage. That's for length of run and voltage drop. I've got 2 CAT6a ready for data, internet, and cameras at the garage/gate end, to go too. NAT will be in the garage (heated), hard-wired back to the house. Making a bit of a sub-network at that end.

Nothing is set in stone, and we're not that gadget hungry, just basics.

I've not thought about EV (although I'm refraining) or solar on the garage (which might be an option) but I'd always thought solar for the garage rather than the house. Question, should I run more CAT6a just in case or am I complicating when I don't need to. I think I've more question to answer before finalising anything. CAT6a I've got enough to run as many as I want, but wasn't planning on any more than a 12 port switch at the house.

Better to run a couple of spare ducts and lengths of CAT whatever now than later.

 

[Onoff]

Bloody pub was shut!

 

[dobbslc]

 

[addjunkie]

Better to run a couple of spare ducts and lengths of CAT whatever now than later.

The data cable canrun in the same duct as the SWA…they actually make it like that…3 cores with a https://www.screwfix.com/p/time-ev-...MI16-tyOiojgMVD5JQBh1vhAkrEAQYBiABEgLUifD_BwE

Why the need to over complicate something fairly simple

 

[Onoff]

The data cable canrun in the same duct as the SWA…they actually make it like that…3 cores with a https://www.screwfix.com/p/time-ev-...MI16-tyOiojgMVD5JQBh1vhAkrEAQYBiABEgLUifD_BwE

Why the need to over complicate something fairly simple

Well aware of the combined SWA/Cat cable thanks.

I was assuming though I need separate data cables for the solar PV and the EV charger?

Thinking to run from the house cu in standalone SWA and two separate Cat cables (PV & EV). Then from the garage cu to the EV charger in 6m of the combined stuff. It will mean I think I'll need to join the Cat cable from the EV charger to one of the of the standalone ones to the house...

 

[sparkysy]

I would always run spare cat5/6 cables in a duct, they can be used for so many applications these days, CCTV, load curtailment, PV import/export measurements as well as internet.
If you think you need 2 put at least 4 in.
It's saved me stress many times going back to jobs, and cat5 is cheap enough if you buy 305m drums of it.

Also solar, you have to be careful of volt drop, it is 1% for solar. Not the usual 5% general circuits & 3% for lighting.
This if the sub main is long it can cause the cable size to become quite large!

Also XLPE cable is 90°C rated, but the switchgear it is fed from and supplying also needs to be capable of the same heat rating for it to comply.
Generally I still calculate using the standard 70°C figures for SWA.
And a lot of gear for correct use with XLPE is hellishly expensive

 

[Onoff]

So as the pub was shut I figured to do some calcs.

I think and hopefully someone will chip in, the purpose of the current transformer on the EV charger is it prevents charging of the EV if there's not the current available?

For some future proofing I'm thinking 10mm² based on:

- 32A for the EV charger
- 31m total run to the EV charger. (25m house cu to garage cu then 6m to the EV charger).
- Volt drop for 10mm² is 4.4 mV/A/m (about 1.9%)

4.4 mV/A/m × 32 A × 31 m = 4.36 V so 1.9%. Well under the 5% for a power circuit.

Tbh 6mm² would probably be fine as the volt drop is just over 3%.

Anyone care to check my maths?

Cheers

 

[Onoff]

Also solar, you have to be careful of volt drop, it is 1% for solar. Not the usual 5% general circuits & 3% for lighting.
This if the sub main is long it can cause the cable size to become quite large!

Also XLPE cable is 90°C rated, but the switchgear it is fed from and supplying also needs to be capable of the same heat rating for it to comply.
Generally I still calculate using the standard 70°C figures for SWA.
And a lot of gear for correct use with XLPE is hellishly expensive

I'd based my calcs on 70⁰C armoured.

Didn't know about the 1%. As I say I know nothing about solar.

How does that then impact my thoughts on a 10mm² supply cable and does it need to be XPLE?

Cheers.

 

[sparkysy]

Ok so a very quick app calculation shows this result!
I would have to sit down and go through it properly to confirm it,
Results based on the cable being 23m of SWA in duct, voltage at 230v and power factor of 0.9.

 

[Onoff]

Ok so a very quick app calculation shows this result!
I would have to sit down and go through it properly to confirm it,
Results based on the cable being 23m of SWA in duct, voltage at 230v and power factor of 0.9.
View attachment 503497
View attachment 503498

Cheers. Is that allowing for future PV on the garage?

 

[sparkysy]

Yes that's a 1% volt drop on the supply cable to the garage, this was calculated for a design current of 32a either way.

 

[Milkybars]

@Onoff not that far from you (DA17 6AB) Cleveland cables dealt with me direct and you can collect if required.
Worked out cheaper than any wholesaler price I was getting quoted elsewhere

 

[Onoff]

@Onoff not that far from you (DA17 6AB) Cleveland cables dealt with me direct and you can collect if required.
Worked out cheaper than any wholesaler price I was getting quoted elsewhere

Erith from memory? Dealt with them for work in the past. Cheers.

 

[Onoff]

Yes that's a 1% volt drop on the supply cable to the garage, this was calculated for a design current of 32a either way.

I presume I can "get away with" 16mm² to the garage cu then smaller to the EV charger?

 

[sparkysy]

I presume I can "get away with" 16mm² to the garage cu then smaller to the EV charger?

Yes, design it as a standard circuit. 6mm would be fine!

 

[RaceDiagnostics]

Excuse the dumb question, why select 1% volt drop Vs 2%?

 

[sparkysy]

No not dumb at all!
That is what is required for solar installations 1% maximum.
To be fair you always try and get the supply feed volt drop as low as possible as this allows more for final circuits this meaning the cable sizes don't become excessive and difficult to terminate.
Our final circuits are 5% for general power and 3% for lighting, this I feel needs changing as we don't use incandescent lighting any more and most equipment now runs on +5 > 230v so is not quite so critical for most applications. (I say most as some it is still important)

 

[MetalMonkey]

Excuse the dumb question, why select 1% volt drop Vs 2%?

You need the lowest possible volt drop as the inverter has to "push" back into the grid, which fluctuates in voltage – based on worse case, if the grid is up at 254V the inverter has to overcome this + any volt drop and it might run out of headroom.

 

[Onoff]

Well these bits are going to tot up, ah well, do it once etc. Just mulling the new garage cu. It'll be from Fusebox. Just fag packet sketching at the mo.

Can I incorporate the MCB I'll need for future PV in this cu or do I need a separate solar PV combiner etc. Keen to keep as neat as possible.