Static or not

[Strickers]

I've picked up some work doing maintenance on a caravan site. The caravan's are what I would class as static but are all fed via a small 30ma RCD protected enclosure onto a 16a single phase BS4343 socket which has to be 30ma protected because its less than 20A.

The supply is for 5 caravan on a 25mm 2 core radial protected by a 100ma RCD.

The supply is therefore not going straight into the caravan and would then be classed as temporary and fall under section 721 of BS7671, which means that it can't be therefore be supplied via a TNCS supply which it is at the momment. The cpc must be split at the socket and the caravan made a TT system via its own earthing system.

Should it be classed as a static or caravan on the strength that its on a BS4343 socket and fall under section 721 or would you still class it as a static caravan and stay under Bs7671 as a whole.

Any comments will be useful.

 

[Deleted member 26818]

One of the reasons Caravans are not allowed to be TN-C-S as I understand it, is due to the fact that there is no guarantee the internal wiring of the caravan is up to scratch.
I think that I would go for TT, unless there's some paperwork stating the internal wiring of each of the caravans are up to scratch.

 

[Engineer54]

I've picked up some work doing maintenance on a caravan site. The caravan's are what I would class as static but are all fed via a small 30ma RCD protected enclosure onto a 16a single phase BS4343 socket which has to be 30ma protected because its less than 20A.

The supply is for 5 caravan on a 25mm 2 core radial protected by a 100ma RCD.

The supply is therefore not going straight into the caravan and would then be classed as temporary and fall under section 721 of BS7671, which means that it can't be therefore be supplied via a TNCS supply which it is at the momment. The cpc must be split at the socket and the caravan made a TT system via its own earthing system.

Should it be classed as a static or caravan on the strength that its on a BS4343 socket and fall under section 721 or would you still class it as a static caravan and stay under Bs7671 as a whole.

Any comments will be useful.

It doesn't matter whether ''static'' or not, PME (TNC-S) cannot supply caravan type installations. This rule applies to both types of park sites, including permanent residential sites. All supplies must be via TN-S or TT.


I take it that main 100mA RCD supplying the 25mm sub-main cable is an S type RCD, ...right??

 

[mike22861]

I work at a caravan park with 25mm 2 core feeding exactly the same boxes (rolec) due to the many inherent glanding problems with earth continuity we found it easier to earth spike at regular intervals then even poor glanding continuity doesn't mean loss of earth and even though the earth loop spec for a 30mA rcd is under 1663 ohms it is rare on large installations not to have several failed RCDs even when regularly tested so as low as possible earth loop keeps it safe (Touch Voltage).

 

[Engineer54]

I work at a caravan park with 25mm 2 core feeding exactly the same boxes (rolec) due to the many inherent glanding problems with earth continuity we found it easier to earth spike at regular intervals then even poor glanding continuity doesn't mean loss of earth and even though the earth loop spec for a 30mA rcd is under 1663 ohms it is rare on large installations not to have several failed RCDs even when regularly tested so as low as possible earth loop keeps it safe (Touch Voltage).

Agree completly with installing a spike at regular intervals.... Shows you know something about TT installations... lol!!!

And as for the observation on RCDs ....I've been saying this for ages here, but the die hard's will not accept the level of RCD failures is High!!!

 

[Strickers]

The RCD covering the radials to the caravans is a 's' type RCD its a merlin gerin with integral isolation, and I have completed the work as Section 721 taking a earth rod directly to plug earth feeding the caravan with loop tested out at 56.6 ohm which being <200 ohms according to Table 41.5 note 2 is an acceptable reading. It's just strange to me that 40 caravan on the site where obviously not installed correctly from the out set the client is now asking why i'm the only electrician in 10 years to point out its wrong.

Cheers for your help guys any further comments.

 

[nickblake]

im a big beliver in every hook up has its own earth rod just my preferance realy and im always wary of RCD's as engineer 54 has said RCD's do fail and even more when subjuct to damp and some times humid conditions like in ip rated enclosure it only takes a heavy rain shower followed by the sun to cause condense on an RCD that in an enclouser see it all the time here .. may be its because i live in wales when it rains it rains

 

[Graeme Harrold]

Cant fault the more the merrier on the earth rods, although max impedance is 1667, I have come across numerous problems with RCD's NOT tripping on 5X when the Ze has been high (>100). This has normally highlighted a glanding deterioration at the box. Didnt help on the last one, the wrong fittings had been used, plus the close proximity to the sea (150m)

 

[Deleted member 26818]

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

 

[nickblake]

Agreed mate do like it to be less than 200 for stability in fact im fussy i like it to be less than 100 and the salt air plays merry hell with conductors infact any metal fittings too ,as you'll know living in the same area graeme

 

[Graeme Harrold]

Find a lot of the sites on the south coast of the peninsula get battered over the winter, plays hell with anything metallic.....

 

[MarkieSparkie]

I've picked up some work doing maintenance on a caravan site. The caravan's are what I would class as static but are all fed via a small 30ma RCD protected enclosure onto a 16a single phase BS4343 socket which has to be 30ma protected because its less than 20A.

The supply is for 5 caravan on a 25mm 2 core radial protected by a 100ma RCD.

The supply is therefore not going straight into the caravan and would then be classed as temporary and fall under section 721 of BS7671, which means that it can't be therefore be supplied via a TNCS supply which it is at the momment. The cpc must be split at the socket and the caravan made a TT system via its own earthing system.

Should it be classed as a static or caravan on the strength that its on a BS4343 socket and fall under section 721 or would you still class it as a static caravan and stay under Bs7671 as a whole.

Any comments will be useful.

Hi Strickers,
BS7671, Section 708 applies to Electrical Installations in Caravan / Camping Parks and Similar Locations.
ESQCR 2002, 9(4), prohibits the use of a TN-C-S supply system to a caravan or similar construction (see 708.553.1.14).
708.530.3 States NOTE: Not more than four socket-outlets should be grouped in one location ...
708.533.1.12 States Each socket-outlet shall be provided with individual overcurrent protection.
708.553.1.13 States Each socket-outlet shall be protected individually by an RCD having Characteristics specified in Regulation 415.1.1 The device shall disconnect all live conductors including neutral.
708.533.1.14 States ... For a TN-C-S system, for a supply with a PEN conductor the protective conductor of each socket-outlet shall be connected to an earth electrode and shall comply with the requirements for Regulation 411.5 for a TT system.

 

[Deleted member 26818]

This is an excerpt from BS7430 the Earthing Code of Practice:
21.10 Mobile (touring) caravans and caravan parks
The electrical protection of persons and livestock using, or in contact with, a caravan has to be reliable since a fault to earth
of equipment within that caravan can result in its frame rising to a dangerous voltage above that of the ground on which it is sited.
Any person then touching any metalwork of the caravan while standing outside is open to the risk of electric shock.
Because of the special hazards associated with caravans, the current Electricity Supply Regulations do not permit the use of PME systems for their supply.
Permanent buildings on a caravan park may be treated as if they are ordinary premises and may be supplied and protected by generally adopted methods.
In such cases the main earthing terminal of an installation which is part of a TN-C-S system may be used.

NOTE Residential caravans which are not normally intended to be moved from a caravan park are regarded as permanent buildings.

 

[i=p/u]

im with you spin, i say ya can tp-q-s as there permenant. you clever chap

 

[mike22861]

you can never have too much earthing on a caravan park its still far safer to bond the frame to earth and spike it. At least you are relying on a good earth path not some cheap rcd that may or may not fail within 10 minutes of you pressing the test button.

 

[Engineer54]

im with you spin, i say ya can tp-q-s as there permenant. you clever chap

If you or Spin can show where it specifically states that a caravan/mobile home (built to the same construction methods as a touring caravan, ie ..Metallic skinned) can be connected on a permanent or temporary basis to a PME (TNC-S) then fine!! But until then, i believe that the exclusion of PME stands for both types of caravan/mobile home's....

The permanent buildings on these park sites relates to the conventionally built club house's, shops, shower blocks and the like... Nothing with wheels on it ...lol!!!

 

[mike22861]

I think it comes down to the terminology I wouldnt expect a caravan fed by a 16A supply to be a permanent residence on our site we have 3 categories permanent residences fed by 63A non RCD supply just as a DNO would supply to a house, permanent sited but not permanent residence supplied by 32A 30mA rcd feed and temporary sitings fed by 16A 30mA rcd feed I would class the 63 supplies as ok for TN-C-S and the rest as not. I still maintain the more earth you can get the better don't be fooled by RCD protection.

 

[nickblake]

Mmm i have to agree with Engineer 54 on this one , its the structure that causes a problem wether it moves or not its still cladded in metal , have you ever tried to open a caravan door when its been connected to a TNCS supply with a neutral fault a nice 120 volt belt which is above the safe voltage so dangerouse ,and its for this reason the supplies have to be TNS or TT

 

[Deleted member 26818]

If you or Spin can show where it specifically states that a caravan/mobile home (built to the same construction methods as a touring caravan, ie ..Metallic skinned) can be connected on a permanent or temporary basis to a PME (TNC-S) then fine!!

I believe that the quote from BS7430, does just that.

 

[Engineer54]

I believe that the quote from BS7430, does just that.

You mean as you quoted above ?? If so, i don't think so. I believe the ''permanent'' buildings they are referring to, are the conventional type buildings found on these caravan/mobile home parks.... Not the over-sized caravans (30 odd feet long) they call mobile homes, complete with wheels. They are built in the same type of construction method as touring caravans, using the shell as part of it's overall integral frame strength.

Now if your talking about the other type of mobile home, those that can be split and moved on low loaders. Fine!! They are wood or composite material framed based, and therefore wouldn't have any restriction as to what type of electrical supply can be provided....
They don't come with wheels either. ...lol!!

 

[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