Garage wiring

murphaph

Hi All,
Not sure if you folks can advise as my house in in Germany but sure I'll ask anyway.

I am soon going to be pouring the foundation for my garage and laying the services to it.

The current setup (house) is:

100A 3 phase supply "mini pillar" -> 5 x 25mm² cable -> 63A SMCB -> Meter -> RCDs -> MCBs.

I laid a 5 x 10mm² (Cu) cable (on the recommendation of the electrician that did the house install, but he's retired now so I'll have to get a new one) from the distribution board (not wired to anything) back out of the cellar and it's buried underground. Distance from house distribution board to planned garage distribution board ca. 10m.

I want to set a 32A three phase CEE socket in the garage as well as the usual lighting and 16A sockets. The 32A could also come in handy if I ever add a Wallbox for a car.

I believe the cross section of the 10mm² means it can't handle 63A so something has to go between the 63A SMCB and the start of the cable feed to the garage to protect it. Is this correct?

What might that be?

In the garage I intend on fitting another sub-distribution board (I have KNX in my house so want to use it in the garage as well for a few things like the roller shutter and I need DIN rails for that and I don't want to be having to go into the house to rest an MCB or RCD due to something in the garage).

If I'm better asking on a German forum just let me know and I'll be off

Steve

You're better asking a German electrician as the regs there, while I assume they are similar to ours, will not be widely known.

Regulation aside, and speaking from theory:

I believe the cross section of the 10mm² means it can't handle 63A so something has to go between the 63A SMCB and the start of the cable feed to the garage to protect it. Is this correct?

The purpose of the 63A breaker is to protect the cable downstream. This would need to be minimum 16sq.

If you have 5x10sq, you need to protect that with a 40A breaker max.

If you are pouring foundations, put in a duct / pipe so you can upgrade the cable in future should you need to.

murphaph

Thx Steve, yeah I will definitely lay an empty duct as well. I'll need a local electrician to sign off on the work anyway but it's good to be armed with some knowledge in advance ;-)

I think I can't just use a "normal" 40A MCB because I would need a 32A MCB in the garage protecting the cable and 32A CEE socket and these are too close together to get selectivity, so I'd potentially trip out the 40A breaker in my cellar before the 32A one in the garage consumer unit and have to traipse into the house to reset it. I think I need another 40A SMCB after the 63A SMCB I already have inside the house consumer unit and then (in the garage consumer unit) an RCD (30mA?) and then a normal 32A MCB (and the other 16A one(s) for the normal sockets).

Does this sound about right? (from theory, not from regs point of view).

gctest50

Upgrade the cable between the house & shed to 5 x 25 now - makes it easy, and more capacity for the future - car charging etc

Qelres.

gctest50 wrote: »

Upgrade the cable between the house & shed to 5 x 25 now - makes it easy, and more capacity for the future - car charging etc

Put it in now anyhow

Upgrading garage supplies isn't really a thing

murphaph

I've toyed with the idea of putting 16mm² in instead of the 10mm² but 25? The main house connection has that cross section and we have an 11kW heat pump to run off it as well. Isn't that a bit much?

I've heard the rapid car charging argument before but I can't see how this can work if everyone on the street has 2 e-cars. The local electrical infrastructure could never handle the load of everyone rapid charging their cars at home at 7pm. I think they will restrict the amount you can draw when e-cars become more common, probably with smart meters or whatever.

To be honest the car is not going in the garage anyway. More of a workshop. The car will go in a carport which is adjacent to the existing utility room so I was just going to lay a duct from a known point outside the cellar to the carport and if rapid charging ever happens for us, we can bore a hole in the cellar wall at that spot and feed another cable directly to the carport wall box directly from main board. But I'm not convinced it'll become a thing due to the network constraints upstream.

16mm² can take 70A when buried directly in the earth I believe. I can't imagine I would ever need more than that. I think the 32A might never even be reached but I'd like to have the possibility of it.

murphaph

Just a short update as I've asked on a German forum.

10sq Cu is allowed to carry up to exactly 63A here @25°;C. This is the "normal working temperature" electricians assume here for domestic installations.

So I'm told the cellar and underground parts are absolutely fine as the assumed working temp is even lower in these areas but some electricians might have a problem assuming 25 degrees for the garage while others would not. The cable must be in free air or laid in the ground for 63A to be an option. It can't be in conduit as the heat can't get away as effectively in conduit. In conduit the max I is therefore lower.

IF an electrician isn't happy with 63A he will have no problem with a 3*50A fuses after the smcb & meter to protect the cable to the garage. This is not selective but as it only protects the cable to the CU in the garage in an extremely unlikely case it doesn't really matter if the smcb trips out before the fuse(s) blow.

50A are more than enough for my single 32A socket requirement so I'm assured the cable will be fine and there's no need to replace it.

Thanks all.