garage Electrics

[Steve]

concerned: for a long run (>2metres), shouldnt his meter tails go into a 25mm² SWA? THEN to the consumer unit?? Are there any regs for this?

 

[keith70]

hi
at the moment there are a pair of wires and an earth that go from the meter into a grey box with a fuse in it(is this a Henley block?)
from this two similar sized wires and an earth run to my CU inside my house( i presume)
would the electrician have to change this "grey box" and put a larger one in so that he could connect to the switched fuse or MCB as ban-all-sheds suggests
just so that i know what the electrician is saying when he quotes
thanks Keith
ps the extension was completed several years ago by a competent builder and electrician etc

 

[Steve]

that box with a fuse is probably a switchfuse or an isolator. This makes life easier, as your spark doesnt need to pull the service fuse (before the meter). Either this or you have got it wrong and you are describing the service head. Does it have metal tags on it that look like seals?

Can you take a photo????? please do try!!!!

 

[keith70]

hi crafty
no it doesnt have tags on it
the box before the meter does so i presume that this is the service head as you say
would take a pic but cant find the camera( bloody kids)
cheers

 

[ban-all-sheds]

It's not in that sequence - the service fuse comes before the meter, not after - see //www.diynot.com/forums/viewtopic.php?p=141310#141310

A service connector block aka henley block aka service splitter is just a high-current capacity junction box made to securely take large cables, i.e. meter tails.

This is a photo of the inside of a single-pole one:

DP ones are also available, so to split the service to feed something in addition to the CU (e.g. a switchfuse, or a small enclosure with MCB) you need a DP block, or 2 SP ones, and they would go in the tails that run between the meter and the CU. Each block or each pole would have 3 cables in it - 1 incoming, 2 outgoing.

 

[DDoyle]

Don't worry about the argument - it happens a lot with B_S whenever he is questioned or challenged.

Ban-All-Sheds, I think your being rather unfair in this thread, nothing that Big-Spark posted was incorrect, he was simply accused of nit picking which he stated he was not. His post was worded very well in my opinion. His final reply I think should be taken with a pinch of salt as he is obviously being sarcastic.

From an outside point of view I found his post helpful and informative, and his comment about retaining the services of a professional electrician was sound. You have chose to critisise him, yet you have actually agreed with his post about the method of doing the job, although you worded it differently.

 

[keith70]

its as crafty says service fuse then meter then switch fuse then wires going to the CU
so if i have got this right the electrician would prob put in a henley block after the switch fuse with a pair of tails to the CU (as now) and another pair to a MCB from which the SWA goes to the garage just as you said in your earlier post ban-all-sheds
i get it now sorry for being so slow but i do like to understand things
hope this topic has been as helpful to other people as it has been for me
at least now i will know what the electrician is talking about when i get a quote off him
just have to find out if the DNO will let him put somthing in their box as previously mentioned
thanks keith

 

[ban-all-sheds]

Ban-All-Sheds, I think your being rather unfair in this thread, nothing that Big-Spark posted was incorrect, he was simply accused of nit picking which he stated he was not. His post was worded very well in my opinion. His final reply I think should be taken with a pinch of salt as he is obviously being sarcastic.

To a large extent, but it wasn't me who saw it as an argument..

From an outside point of view I found his post helpful and informative, and his comment about retaining the services of a professional electrician was sound. You have chose to critisise him,

How odd - when I look back at page 1 I see posts from crafty & l.spark, not from me. Maybe you're eyes work differently to mine.

yet you have actually agreed with his post about the method of doing the job, although you worded it differently.

Mostly.

Don't agree with RCD protection for the cable.

 

[DDoyle]

Ban-All-Sheds, I think you have misinterpreted what I meant, I did not mean to imply that you had argued with him, simply that your comment gave the impression that he caused the arguement that had been referred to and it was this I felt unfair as the comments he recieved were unecessary, but I do accept you did not make them.

Regarding the RCD protection of the cable, Big_Spark is correct to recommend this and to support this I would refer you to Regulation 471-08-01 and the details of sub-paragraph (i) which concerns itself with "Installations and Locations of increased shock risk, such as those is Part 6".

Now Part 6 refers to Special Locations, and although a supply to a domestic garage may be stretching this definition, the idea of protecting the cable by use of an RCD is sound as this would reduce the risk to any person who inadvertantly dug up the cable at a later date or worked on the live side of the supply in the Garage.

 

[Spark123]

There is no requirement to RCD protect underground cables (TN systems), 30mA RCD protection is however required for socket outlets reasonably expected to supply equipment outdoors. RCDs with a trip rating greater than 30mA are of little use in supplementary protection against direct contact.

 

[DDoyle]

Spark123, you are correct in that there is no regulation that specifically deals with the situation spoken of in this thread concerning a buried cable, however I think this is were interpretation of the Regulations that are there is important, which is why I refered Ban-All-Sheds to Regulation 471-08-01. If we treat the supply to an outbuilding as a special location then the installation should meet the requirements, albeit slightly modified, for such a building/location as defined in BS7671.

The installation of RCD or RCBO protection inside this special location, in this case a garage, goes without saying as it is a requirement, however should not a good installer also consider the implications and the possibility, regardless of how remote, that the cable may be damaged by activeties in the garden at some point in the future. Small armoured cables are easily damaged by gardening equipment and it is incumbant upon any installer to consider the risks and hazards when the cable is installed. As such I do agree that protecting the cable with a suitably rated Type S RCD is appropriate as this would protect any persons causing damage to the cable, but also protect the overall integrity of the main supply should it not be connected into the Main Consumer Unit.

Obviously different installers will look at this differently, and different situations will require different solutions, but I do think it is right to consider this and then modify the plan to suit the installation in question.

 

[ban-all-sheds]

should not a good installer also consider the implications and the possibility, regardless of how remote, that the cable may be damaged by activeties in the garden at some point in the future. Small armoured cables are easily damaged by gardening equipment and it is incumbant upon any installer to consider the risks and hazards when the cable is installed. As such I do agree that protecting the cable with a suitably rated Type S RCD is appropriate as this would protect any persons causing damage to the cable,

A 300mA Type-S RCD will provide no personal protection whatsoever. That's why RCD protection for situations of increased risk of shock have to be 30mA or less.

If somebody sticks a fork through the cable, his protection comes from the fault current operating the OPD.

 

[DDoyle]

A 300mA Type-S RCD will provide no personal protection whatsoever. That's why RCD protection for situations of increased risk of shock have to be 30mA or less.

If somebody sticks a fork through the cable, his protection comes from the fault current operating the OPD.

We will have to agree to differ on this point as I have seen many occasions where buried cables have suffered Neutral-Earth faults that have not operated any overcurrent devices, but left to their own devices, they create more problems in the longer term. It was you that mentioned a 300mA device, I know Big_Spark did in his post, so I am assuming this is why you mentioned it, now the rating may be open for debate, but I still beleive that buried cables should be Type S RCD protected.