Static or not

[mike22861]

Actually all the caravans I am referring to are the 30ft variety touring caravans have to be fed by 30mA rcd supplies no more than 3 to an individual RCD and for info even the 3 bedroom 2 bathroom log cabins have wheels although we remove them after siting and we feed them with 32A non rcd supplies as they have their own split load dist boards fed from a T-N-S system.

 

[IQ Electrical]

Shouldn't each socket-outlet have individual RCD protection?

Spot on, the RCD should disconnect the neutral too.

Just to clarify though, the requirements of section 708 and 721 do not apply to mobile homes or residential park homes or transportable units.

 

[mike22861]

Yes I should have pointed out they are 2 pole RCDs not single pole RCBOs it's also quite unnerving how many times i get asked if an RCD rated at 63 or 32 amps etc is also an MCB to I just sigh and point out its the current rating for max in use amperage and suggest they may try a different job.

 

[Deleted member 26818]

I'm sorry, but this is a British Standard, they don't use a word for one thing, then use the same word for something else entirely different.
This section is headed 21.10 Mobile (touring) caravans and caravan parks.
I would not accept that a mobile home designed to be split and then transported on low loaders as being a Mobile (touring) caravan.
Now in my experience, these British Standards usually define the terms and nomenclature used.
Here is the definition of a caravan as defined by BS7430:
3.2
caravan
trailer leisure accommodation vehicle, used for touring, designed to meet the requirements for construction and use of road vehicles

I don't belive that a mobile home designed to be split and transported on low loaders would meet the requirements for construction and use of road vehicles.
I further don't believe that after having defined the meaning of the word caravan, that the Standard would then use the word for anything other than as defined.
As such where the word caravan is used in the note, it is refering to one with wheels and is designed to be towed behind a vehicle.

 

[IQ Electrical]

Spin, if you were responding to my post on exemptions, I was quoting from Guidance Note 7.

 

[Deleted member 26818]

Spin, if you were responding to my post on exemptions, I was quoting from Guidance Note 7.

No I was responding to Engineer 54.

 

[Engineer54]

Spin,

I am thinking purely from a logical stand point. A mobile home is of the same construction as a touring caravan, both use the metallic shell as the main strength of it's frame. If you exclude one (touring caravan) from the use of a PME derived supply because of enhanced hazard, because of it's construction method, then the surely the other type, (mobile home) will have exactly the same level of hazard as the touring caravan.

The fact that it's sited on a semi permanent location is, or should be irrelevant, the perceived hazard remains the same. Now if you are right, and these over-sized caravans ''Can'' be connected to a PME supply then we have yet another contradiction within BS7671.

By the way, ...Rarely are these 30+ feet mobile homes transported on it's own wheels, behind a towing vehicle, they are generally transported on low loader trailers, just as the split mobile homes are.

 

[Deleted member 26818]

It's not the construction that is the hazard, but the method of connection.
A touring Caravan, or Motor Caravan is designed for an ordinary person to connect and disconnect from a pitch connection.
Whereas a Mobile home, Residential Park home, or (as refered to in BS7430) residential Caravans which are not normally intended to be moved, are not.
When a touring Caravan or Motor Caravan is connected to a pitch supply by an ordinary person, there is no I&T conducted to ensure disconnection times are met, that protective conductors are continuous, there is no check to ensure extraneous-conductive-parts are bonded etc.
Wheraes when a Mobile home etc. irrespective of it's method of construction is connected, just as when a connection is made to a brick built dwelling, a competent Electrician should be involved, and appropriat I&T should be conducted.
As such the requirements of Section 721 are not applicable.
I was not aware when I posted the quote from BS7430, that the Caravans in question are not the touring type, but are Residential.
However such would explain why in the past, no special considerations have been made, the Regulations don't require any.

 

[mike22861]

Just as a point mobile homes semi permanent are required to have a PIR or in new parlance an electrical condition report when they are moved and reconnected they are also required to have an annual PIR if they are to be hired.All mobile homes we site are given a PIR after connection. It's amazing how many times RCDs fail testing, on a caravan site there are probably many many more RCDs than domestic guys come across.I wouldnt trust my life to an RCD. Just as an aside to BS7671 I have a system that runs 600v chopped DC at 20KHZ in water it is protected by a 9mA earth leakage detector and a continuous insulation test that trips if below 1.5Mohms. Would you go near it if protected by a commercial 30mA RCD

 

[Engineer54]

It's not the construction that is the hazard, but the method of connection.
A touring Caravan, or Motor Caravan is designed for an ordinary person to connect and disconnect from a pitch connection.
Whereas a Mobile home, Residential Park home, or (as refered to in BS7430) residential Caravans which are not normally intended to be moved, are not.
When a touring Caravan or Motor Caravan is connected to a pitch supply by an ordinary person, there is no I&T conducted to ensure disconnection times are met, that protective conductors are continuous, there is no check to ensure extraneous-conductive-parts are bonded etc.
Wheraes when a Mobile home etc. irrespective of it's method of construction is connected, just as when a connection is made to a brick built dwelling, a competent Electrician should be involved, and appropriat I&T should be conducted.
As such the requirements of Section 721 are not applicable.
I was not aware when I posted the quote from BS7430, that the Caravans in question are not the touring type, but are Residential.
However such would explain why in the past, no special considerations have been made, the Regulations don't require any.

Well explained Spin....

And there was i, thinking the exclusion was down to the enhanced hazard of a faulty neutral earth on a caravan/mobile home, that is basically totally enclosed in a metallic shell!!

 

[Engineer54]

Just as a point mobile homes semi permanent are required to have a PIR or in new parlance an electrical condition report when they are moved and reconnected they are also required to have an annual PIR if they are to be hired.All mobile homes we site are given a PIR after connection. It's amazing how many times RCDs fail testing, on a caravan site there are probably many many more RCDs than domestic guys come across.I wouldnt trust my life to an RCD. Just as an aside to BS7671 I have a system that runs 600v chopped DC at 20KHZ in water it is protected by a 9mA earth leakage detector and a continuous insulation test that trips if below 1.5Mohms. Would you go near it if protected by a commercial 30mA RCD

Fully agree with you there on the total reliance of an RCD device Mike!! Which is why i consider this BS 7671 200 ohm Ra level for a TT system, as a total farce.

 

[Strickers]

Cheers for all your comments not looking forward to talking to client tomorrow and explaining that all there supplies need changing to TT. Well bit of work for me.

 

[mike22861]

We try and get earth spike Ras below 10 ohms either by multiple spiking or other earth plate arrangements. BS 7671 doesn't give a calculated reason for the 200 ohm other than its likely to be unstable above this in my experience and Ra of 200 ohms is practically unacceptable it would certainly lead to a touch voltage over 50V which is what i thought the regs were all about keeping touch voltage below 50V