Rcd protection for caravan hook ups

[North88]

I'm sure this will have been covered before but please bear with me. Have been asked to replace a main Distribution board for a fairly small caravan site and add in some new hook ups ( space for 8 x 16A sockets currently but upgrading to 12 x 16A and a 32A).

Now this is all fed from one 100A 1361 type 2 supply which i have made client aware might struggle to cope as there is already a small shower block fed from here also... alas he would like to go ahead all the same.

Anyway basically all hook up points have there own RCBOs for each socket and the shower block an RCD in its sub main board. Can the supplies from the main DB to the hook ups and shower block just be connected to Mcbs and a 100A Main switch stop to nuisance tripping or do these supplies also have to be Rcd protected. Swa cables are all buried and will be earthed at mains end.

Thanks folks.

 

[pc1966]

Assuming the supply is TN then you don't (usually) need RCD for the SWA sub-mains. Even for TT it is needed for disconnection on faults due to high Ze so can be delay type.

Feeding blocks of RCBOs from a MCB would "manage" overload to a degree on a segment by segment basis, but you will have poor selectivity on any faults. Basically the RCBOs would not trip fast enough in most cases to give the MCBs a chance.

The main switch would have to be 100A (or more) due to the supply fuse being 100A, but that will make zero difference to overload protection.

If you wish to prevent the DNO fuse going due to the suspicion of a total significantly over 100A you would need to use a fancy electronic RCCB set to cut off very fast, and probably at around 80A thermal limit as well (not cheap). Again, not going to be good on selectivity but might be slightly less bothersome than the DNO having to come out to replace fuses in the middle of the night, etc.

 

[littlespark]

100A single phase supply?

I wonder how hard it would be for DNO to triple up?

300 across 3 phases better than 100.

 

[North88]

100A single phase supply?

I wonder how hard it would be for DNO to triple up?

300 across 3 phases better than 100.

Yeh single phase mate I’m really not sure what sort of a load a modern caravan takes. I guess that will vary greatly between user also.

 

[North88]

Assuming the supply is TN then you don't (usually) need RCD for the SWA sub-mains. Even for TT it is needed for disconnection on faults due to high Ze so can be delay type.

Feeding blocks of RCBOs from a MCB would "manage" overload to a degree on a segment by segment basis, but you will have poor selectivity on any faults. Basically the RCBOs would not trip fast enough in most cases to give the MCBs a chance.

The main switch would have to be 100A (or more) due to the supply fuse being 100A, but that will make zero difference to overload protection.

If you wish to prevent the DNO fuse going due to the suspicion of a total significantly over 100A you would need to use a fancy electronic RCCB set to cut off very fast, and probably at around 80A thermal limit as well (not cheap). Again, not going to be good on selectivity but might be slightly less bothersome than the DNO having to come out to replace fuses in the middle of the night, etc.

Thanks mate it’s one of those ones I sort of wish I hasn’t got involved with!

So do you believe the individual rcbos for each socket would trip aswel as the mcb for an overcurrent fault?

I believe the 4x16A supplies are 6mm on 32amp mcbs at the moment. Depending on length of run they could possibly go onto 40A mcb as they are buried?

Cheers

 

[littlespark]

Well, are we talking touring hookups or statics? Is the 32A for a lodge?

Statics and lodges may have additional kitchen appliances not found in tourers, so you can work out a typical load.

Notwithstanding customers bringing their own 3kW kettles in from home, or electric blow heaters when there’s gas heating in the units.

Can’t plan for the idiotic!

 

[North88]

Well, are we talking touring hookups or statics? Is the 32A for a lodge?

Statics and lodges may have additional kitchen appliances not found in tourers, so you can work out a typical load.

Notwithstanding customers bringing their own 3kW kettles in from home, or electric blow heaters when there’s gas heating in the units.

Can’t plan for the idiotic!

The 32 amp is for a static. The 12 x 16 amp will be tourers I believe. Also a 10mm supply to a portacabin/shower block that basically has one 9kw (give or take) shower.

I have advised I have concerns about the load upfront.

 

[UNG]

I would suggest that if you limit the supplies to the tourers to 10A so it gives a little bit of margin on the supply you may stand a chance of it working, as a caravanner it is very rare to get a 16A hook up most are 10A and in Europe you are very often on a 6A hook up
All protection devices will carry a little bit of overload for a time before tripping so a 10A MCB will keep it within the 16A limit likewise with the statics it may be possible to use a 25A rather than the 32A

 

[brianmoooore]

10A type C is the usual for a touring caravan supply, and consumption above about 3 - 4 A will normally only be for short periods with the periods of high consumption being more spread out, compared to a row of houses, where everyone might switch on a kettle during a TV advert break.

 

[North88]

8 of the 16s are already present and he has the new hook ups already. I will advise once again with my concerns and maybe I will get a job out of it to install new 10a rcbo hook ups to existing perhaps.

 

[brianmoooore]

Note that the new hook ups are required to have interlocked switches.

 

[North88]

Note that the new hook ups are required to have interlocked switches.

Cheers I didn’t realise that mate. Does that rule just apply to new install ones?

 

[brianmoooore]

Yes, only new ones, as long as existing were installed in compliance with the regs at the time.
They're advertised as "18th edition compliant", so presumably it was introduced with the 18th.
Just setting up a new mini site, and they're a LOT more expensive than the older type.

 

[North88]

Yes, only new ones, as long as existing were installed in compliance with the regs at the time.
They're advertised as "18th edition compliant", so presumably it was introduced with the 18th.
Just setting up a new mini site, and they're a LOT more expensive than the older type.

No surprise there!

 

[brianmoooore]

shower block that basically has one 9kw (give or take) shower.

I have advised I have concerns about the load upfront.

Can't imagine one shower being adequate for 12 touring pitches, and no diversity is allowed on water heaters, so there's over a third of the available load being used up by this one device.
Be far better setting up a pressurised hot water cylinder which will be capable of supplying more than one shower, plus hand basins etc..
3kW load, so another 24A or so "set free" to be used elsewhere in the load calculations. Better still would be a LPG or oil boiler to heat the water (and much cheaper to run, if not install.)