Pme again with workshop help please

[Blue Duck]

Nothing. TT is a rubbish system if you ask me. If people want to trust their lives to an RCD, the most unreliable piece of junk the world has ever seen, then go right ahead.. BUT, the OP was worried about his assessment, and so does not want to get into anything that might be seen as "controversial" by the assessor...

john..

I disagree.

purely because your in control of your earthing and not exposed to the copper saving disciplines your distribution network operator.

@Ampsyaman just nail a bit of t&e to the fence - as long as your funds have cleared prior to your assessment you should be fine. 

:innocent

 

[apprentice87]

Was just thinking about a TT & how's it's fed and at the start of its life as it enters the house you have a timed delay unit fitted before the c/u not up the poll in the street, am I thinking wrongly here sorry if I am, 

You would not.. You WOULD fit a TD RCCB for example, at the feed end of a submain, to provide discrimination with other standard devices in series with it further down the line. For example, the submain might feed five sheds in your garden, and you would not want a fault in one shed to shut off the supply to all five sheds, so you would feed the submain with a TD one and fit standard ones to the Cu's in the sheds.

You would NOT have a TD RCD protecting the CU in your house, it would not be permitted, it would have to be a standard one in order to protect against shock hazards.

john..

 

[Duane B]

Lol, funny as f*** that comment, but being serious can anyone give some direction on this, if no assessment  I'd just export it for what it is as most other electricians do daily, 

But it would be a great skill curve to nail this down correctly and safely, I'll buy the spike kit if I have to even for my fluke, I'm sure I drive the biggest stake possible in, or 2 x in parallel line of sight  with each other

 

[Sidewinder]

Ampsayman,

If you are using parallel electrodes, then they need to be a prescribed distance apart.

You need to refer to BS7430 to ensure that the earthing you provide for the TT system is correct.

 

[Manator]

@Ampsyaman this is a problem with doing jobs for assessment and doing everyday jobs. If the NICEIC came and requested to view some installs you had done would they find them all to comply? or just the few you want to show them?

As Sidewinder says there are other standards and regulations outside BS7671 that you should be aware of if you are doing this work.

There is also a difference in exporting and extending, a good understanding of earthing systems should be a prerequisite of designing any installation.

 

[Duane B]

Yeah clocked that one already, most homes have 1 x but as per previous notes just after some real guidance here on this installation 

 

[Evans Electric]

Having worked in a big city all life I find TT  a pain in the do-dah  .

We do get TT in the city , mainly because the network earthing is breaking down.      We have a customer with 6 yes six  rods in and still a poor reading .  

Forget the time delay RCD altogether  Ampy, you don't need it .

Everyone on here will have their own version of this job , here is mine ,

Replace the RCBO with an MCB at the origin.

Joint the cable through to the shed .

Stick a 3 way metal board in there with an RCD main switch.

Wire the rest in the proper manner.

Test it

Wheel out the NIC man .

 

[Duane B]

I got other jobs I can go out to wink wink wink but as at my  home thought be more chilled etc. And thought be a little job to practice and learn some new skills apart from all the standard stuff, 

 

[apprentice87]

1, Get some 2 core SWA

2, Run it out to the shed

3, Obviously earth the armour at the house end by terminating the cable in a proper gland into a proper accessory,

4, Obviously make sure the OCPD for the cable is suitable,

5, Terminate the cable in the shed having cut back the armour a little way [so as to insulate it from the accessory [CU, whatever] in the shed, and use a nylon stuffing gland, or I do believe you can get a proper insulating gland to do this.

6, knock in one rod

7, fit a proper 30mA rcd, in your presumably, not only insulated, but non combustible CU

8, test the whole lot and then forget about it!!

john..

 

[Duane B]

Having worked in a big city all life I find TT  a pain in the do-dah  .

We do get TT in the city , mainly because the network earthing is breaking down.      We have a customer with 6 yes six  rods in and still a poor reading .  

Forget the time delay RCD altogether  Ampy, you don't need it .

Everyone on here will have their own version of this job , here is mine ,

Replace the RCBO with an MCB at the origin.

Joint the cable through to the shed .

Stick a 3 way metal board in there with an RCD main switch.

Wire the rest in the proper manner.

Test it

Wheel out the NIC man .

Export the pme, wire test it result it, 

 

[steptoe]

You would not.. You WOULD fit a TD RCCB for example, at the feed end of a submain, to provide discrimination with other standard devices in series with it further down the line. For example, the submain might feed five sheds in your garden, and you would not want a fault in one shed to shut off the supply to all five sheds, so you would feed the submain with a TD one and fit standard ones to the Cu's in the sheds.

You would NOT have a TD RCD protecting the CU in your house, it would not be permitted, it would have to be a standard one in order to protect against shock hazards.

john..

I have a TD RCD protecting my CU in my house, what's wrong with that,?

Actually, it protects another 2 circuits as well, what's the problem,?

 

[Sidewinder]

I have a TD RCD protecting my CU in my house, what's wrong with that,?

Actually, it protects another 2 circuits as well, what's the problem,?

Mine is similar Steps, but it's the CU & one circuit, the rest are on a single 30mA.

CBA to change it as it's been in so long, it's a pain, but I can live with it until I can get time to change it.

 

[steptoe]

Nothing. TT is a rubbish system if you ask me. If people want to trust their lives to an RCD, the most unreliable piece of junk the world has ever seen, then go right ahead.. BUT, the OP was worried about his assessment, and so does not want to get into anything that might be seen as "controversial" by the assessor...

john..

John,

As much as I admire you, and think you have a usually very good knowledge of electrical systems,

It's answers like this that show up your very limited knowledge in these things,

TT us the best most reliable earthing system there is,

do you rely on the garage telling you the brakes on your car are good each time you take it in for a service,? Or do you make a judgement everytime you use them,? 

TN is relying on the DNO to tell you the earth is good, even though they never check it,! 

Posts like this are simply proof that a little knowledge can be a very dangerous thing.

 

[apprentice87]

I have a TD RCD protecting my CU in my house, what's wrong with that,?

Actually, it protects another 2 circuits as well, what's the problem,?

Nothing as you presumably have also got standard ones or RCBO's protecting socket circuits etc,

john..

 

[steptoe]

Mine is similar Steps, but it's the CU & one circuit, the rest are on a single 30mA.

CBA to change it as it's been in so long, it's a pain, but I can live with it until I can get time to change it.

I actually installed mine <5years ago for a purpose. 

 

[steptoe]

Nothing as you presumably have also got standard ones or RCBO's protecting socket circuits etc,

john..

I've got a sub main protected by nothing but the TD, separate from the other circuits mentioned,

But you made a sweeping statement saying a TD shouldn't/couldn't be used,

Oh, I also have a self combusting CU fitted under my stairs, but, that's another story, I'd imagine by the time I finish and need to notify PartP will be down to only new supplies by then, :slap

 

[apprentice87]

John,

As much as I admire you, and think you have a usually very good knowledge of electrical systems,

It's answers like this that show up your very limited knowledge in these things,

TT us the best most reliable earthing system there is,

do you rely on the garage telling you the brakes on your car are good each time you take it in for a service,? Or do you make a judgement everytime you use them,? 

TN is relying on the DNO to tell you the earth is good, even though they never check it,! 

Posts like this are simply proof that a little knowledge can be a very dangerous thing.

Hi Steps, I agree with what you say 100% TT is obviously more reliable, unless the world falls off the end of your rod, AND, TT would be FAR preferable to relying on the DNO and their not too clever wiring... BUT for one thing... Look at the failure rates for RCD's.. MUCH MUCH more likely to have one of them fail, than a problem with the DNO supply.....

john...

I've got a sub main protected by nothing but the TD, separate from the other circuits mentioned,

But you made a sweeping statement saying a TD shouldn't/couldn't be used,

Oh, I also have a self combusting CU fitted under my stairs, but, that's another story, I'd imagine by the time I finish and need to notify PartP will be down to only new supplies by then, :slap

Hi Steps, Yes i know i did, but in the context that the OP was referring to!!!!

john..

 

[Sidewinder]

I've got a sub main protected by nothing but the TD, separate from the other circuits mentioned,

...

Presumably you have some over current protection in addition to the TD, same as I have on the sub-main to my garage.

 

[steptoe]

Presumably you have some over current protection in addition to the TD, same as I have on the sub-main to my garage.

Yes,

But the fact remains,

You CAN and SHOULD (if required) use a TD to protect a CU, it's got nothing to do with how you protect the final circuit.

That's a totally different matter. 

 

[M107]

1, Get some 2 core SWA

2, Run it out to the shed

3, Obviously earth the armour at the house end by terminating the cable in a proper gland into a proper accessory,

4, Obviously make sure the OCPD for the cable is suitable,

5, Terminate the cable in the shed having cut back the armour a little way [so as to insulate it from the accessory [CU, whatever] in the shed, and use a nylon stuffing gland, or I do believe you can get a proper insulating gland to do this.

6, knock in one rod

7, fit a proper 30mA rcd, in your presumably, not only insulated, but non combustible CU

8, test the whole lot and then forget about it!!

john..

With regard to number 5 above.................How would you test for Zs ?

I would be inclined to terminate using the correct gland into an insulated box, taking the tails on through into the cu & set up cu as TT.

 This way you have you submain circuit cpc(armour) at the insulated box for a Zs reading.