Urgent help please, I'm stuck away from my regs books with only a phone and poor net

[Electricianhow]

Hi guys, I'm new to this so go easy with me lol


iam stuck in Brazil away from my regs books and contact of other knowledgable guys I use but am in urgent need of a question being answered please!


i recently converted two flats, one on top of the other, into a two story house.


>we only kept the bottom floor supply so I ran tails up to the db covering the top floor, and terminated them in a Henley block.   The installation goes like this......main supply feeds Henley block.....Henley block has 2 sets of tails....first to the ground floor dab, second to the first floor db.


>In my absence I have been travelling for 6 weeks, the customer has had another electrician in who stated this


"However, while he was there he noticed that the length of cable  between the mains under the stairs on the ground floor, and the fuse board on the first floor, was such that it should have had an intermediate sub main fitted to cover the risk of a power surge."


>is is this true? I can't see how having a sub main, with say 80a main switch adds any more protection that the main switch already in the upstairs board? I have never had this come up on any of my yearly inspections either, and everyone here knows how on point the inspectors are!!!


>Can someone tell me is this true and do I need to return to install this, I can see a benefit for isolation of dab only, not for surge protection?


many thanks


Howard

 

[telectrix]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

you should protect the tails to upstairs with a switch fuse In < In of the supply fuse. e.g for a 100A supply fuse, you fit a 80A sw.fuse.this prevents a fault on those tails taking out the dNO fuse.

 

[UNG]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

How long are the tails and if longer than 2 -3 metres what fault and overcurrent protection do they have

 

[Jay Sparks]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

Hi guys, I'm new to this so go easy with me lol


iam stuck in Brazil away from my regs books and contact of other knowledgable guys I use but am in urgent need of a question being answered please!


i recently converted two flats, one on top of the other, into a two story house.


>we only kept the bottom floor supply so I ran tails up to the db covering the top floor, and terminated them in a Henley block. &nbsp; The installation goes like this......main supply feeds Henley block.....Henley block has 2 sets of tails....first to the ground floor dab, second to the first floor db.


>In my absence I have been travelling for 6 weeks, the customer has had another electrician in who stated this


"However, while he was there he noticed that the length of cable &nbsp;between the mains under the stairs on the ground floor, and the fuse board on the first floor, was such that it should have had an intermediate sub main fitted to cover the risk of a power surge."


>is is this true? I can't see how having a sub main, with say 80a main switch adds any more protection that the main switch already in the upstairs board? I have never had this come up on any of my yearly inspections either, and everyone here knows how on point the inspectors are!!!


>Can someone tell me is this true and do I need to return to install this, I can see a benefit for isolation of dab only, not for surge protection?


many thanks


Howard

The "main switch" in the upstairs board is merely for isolation! It does not offer overload protection!! If your main feed is over 3 meters then it is advised to protect it with a switched fuse spur, of around 80A as Tel suggested.

The feed may also need protecting by an RCD or containment depending on install method and type of cable you have used.

Jay

 

[Darkwood]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

RCD?...That was may first thought also...you state tails but don't define the cable type if the upstairs supply is not mechanically protected then depending on your installation route you may also need RCD protection which is poor design..

A sub-main with mechanical protection if required to negate the need for a upstream 30mA rcd would be the best method and if over the 2-3m allowed for direct meter connection then as stated above a upfront fused isolation is required.

This is in both your on-site guide and your regs and although you don't have them handy to reference them at present you should really be referring to them when you did the job.

What is the cable and how is it installed (buried, surface ducted etc)?

 

[Electricianhow]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

Ok thanks for clearing that up.

the cables are double insulated 25m2 tails, run in trunking for mechanical protection.

I do not believe the run is over 3 m but will check when I am back and if needed I will install a switched fused isolator.

thanks for all your help

 

[Knobhead]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

Brazil works to NEC regs 110/220V distribution.

What the hell are you prattling on about? BS7671 is bog all use.


Just admit you’ve f**ked a job up in the UK.

 

[Carlosfandango]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

Brazil works to NEC regs 110/220V distribution.

What the hell are you prattling on about? BS7671 is bog all use.


Just admit you’ve f**ked a job up in the UK.

He's already said hes in brasil travelling so presumably he ****ed this job up before he left!

 

[Richard Burns]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

433.2 Position of devices for protection against overload
433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be
installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the
installation.


433.2.2 The device protecting a conductor against overload may be installed along the run of that conductor
if the part of the run between the point where a change occurs (in cross-sectional area, method of installation, type
of cable or conductor, or in environmental conditions) and the position of the protective device has neither branch
circuits nor outlets for connection of current-using equipment and fulfils at least one of the following conditions:
(i) It is protected against fault current in accordance with the requirements stated in Section 434
(ii) Its length does not exceed 3 m, it is installed in such a manner as to reduce the risk of fault to a minimum,
and it is installed in such a manner as to reduce to a minimum the risk of fire or danger to persons (see also
Regulation 434.2.1).
433.3 Omission of devices for protection against overload
This regulation shall not be applied to installations situated in locations presenting a fire risk or risk of explosion or
where the requirements for special installations and locations specify different conditions.
433.3.1 General
A device for protection against overload need not be provided:
(i) for a conductor situated on the load side of the point where a reduction occurs in the value of currentcarrying
capacity, where the conductor is effectively protected against overload by a protective device
installed on the supply side of that point
(ii) for a conductor which, because of the characteristics of the load or the supply, is not likely to carry overload
current, provided that the conductor is protected against fault current in accordance with the requirements of
Section 434
(iii) at the origin of an installation where the distributor provides an overload device and agrees that it affords
protection to the part of the installation between the origin and the main distribution point of the installation
where further overload protection is provided.

The bits in bold are relevant: You need over current protection unless the distributor agrees their fuse provides protection at the origin, normally the DNO specify the 3m rule of 433.2.2.(ii).
This means that tails longer than 3m should have overcurrent protection over and above that provided by the DNO as they do not tend to agree that their fuse can protect an extended length of cable.
However I would not try to get discrimination against the supply fuse, just assume it is for overload and not fault current.
The power surges approach sounds like they mean overcurrent, but that they do not necessarily use the correct terms when explaining to customers.

 

[Knobhead]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

He's already said hes in brasil travelling so presumably he ****ed this job up before he left!

Ooopps.

I've put my gasses on now.

I was going to offer to send him NEC 2011

 

[PEG]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

For gods' sake,Tony,stop sitting on the fence and tell it like it is...:stooge_curly:

 

[Darkwood]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

Ok thanks for clearing that up.

the cables are double insulated 25m2 tails, run in trunking for mechanical protection.

I do not believe the run is over 3 m but will check when I am back and if needed I will install a switched fused isolator.

thanks for all your help

So your telling me from the meter to the upstairs flat is not more than 3m in your honest opinion .... don't treat us like idiots or we will respond at the same level ... leaving the henley block and getting to the ceiling would be 2m on average so you saying the DB for upstairs flat is directly above the mains and less than a meter above the floor as it feeds through?..:6:

 

[Pete999]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

Brazil works to NEC regs 110/220V distribution.

What the hell are you prattling on about? BS7671 is bog all use.


Just admit you’ve f**ked a job up in the UK.

What Tony said just now, not what Tony said yesterday

 

[mechelec]

Re: Urgent help please, I'm stuck away from my regs books with only a phone and poor

you should protect the tails to upstairs with a switch fuse In < In of the supply fuse. e.g for a 100A supply fuse, you fit a 80A sw.fuse.this prevents a fault on those tails taking out the dNO fuse.

That will not necessarily achieve discrimination.
What do you fit in the switch fuse if the DNO fuse is 60A ?
I would fit a fuse in the SWF suitably sized to protect the tails and submain cable used.