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[davesparks]

Agreed. I was just taught to use the table over adiabatic on new work but perfectly acceptable if the calcs stack up.

Why? So that you can throw money down the drain oversizeing cpcs?

 

[rattlehead85]

Just had it pulled on me on numerous occasions over the adiabatic but still your point is very valid.

 

[davesparks]

How can you apply the adiabatic equation to size an earthing conductor on a tn-c-s when it is supposed to be sized in accordance with the sizing of the main protective bonding. The adiabatic equation is used on tn-s & t.t installations and normally is used to confirm adequacy of existing earthing conductors on said existing installations. For new work the relevant tables in BS7671 for sizing of protective conductors in tn-s / t.t installations should be used.

The adiabatic equation is used for all cpcs including the earthing conductor on all installations. In addition to this the earthing conductor of a PME installation must also meet the requirements of a main bonding conductor.

Why do you say the table should be used in preference to calculation? As far as I know there is no technical reason for this.

 

[davesparks]

Just had it pulled on me on numerous occasions over the adiabatic but still your point is very valid.

So what? People have attempted to pull me up on all sorts of things yet come unstuck when they can't back it up with proof.

 

[rattlehead85]

So what? People have attempted to pull me up on all sorts of things yet come unstuck when they can't back it up with proof.

Im not arguing your point im just saying how i was asked to apply the regs on certain jobs by supposedly more tech people than myself i.e electrical surveyors. I agree with what you are saying.

 

[1983]

Spoke to nic today regarding the situation he told me that if it meets the adiabatic equation then it's all good. my pfc came to 2.55ka so looks like a new earth 10mm needs to be pulled in. If I take 5 readings of pefc or psc why do they keep changing I got between 2.3ka up to 2.8ka on psc

 

[1983]

Had argument with my boss today regarding pulling in a 10mm earth from main intake to flat ccu he goes if the main bond to gas and water is 10mm and goes to main intake met why don't I just get the 10mm earth off there in to the ccu met to make it 16mm as it already has 6mm. I told him it's like bonding from ccu met to gas or water. needs to go direct to intake met he told me just f do it so I told him no and I will refuse to sign it as satisfactory

 

[davesparks]

Had argument with my boss today regarding pulling in a 10mm earth from main intake to flat ccu he goes if the main bond to gas and water is 10mm and goes to main intake met why don't I just get the 10mm earth off there in to the ccu met to make it 16mm as it already has 6mm. I told him it's like bonding from ccu met to gas or water. needs to go direct to intake met he told me just f do it so I told him no and I will refuse to sign it as satisfactory

Why does it have to go directly to the intake?

 

[rattlehead85]

The earthing conductor size is calculated by the adiabatic equation. This size is then divided by 2 to get the bonding size.

The bonding in a PME supply is related to the supply neutral, but not all TNCS is PME.

I am not your son! I find it insulting and derogatory that you would call me such. Please don't call me that, or any other derogatory name you can think of.

Think you'll find malcolmsanford has a valid point mate. And i do notice you like to argue and pull everybody up on here. End of the day people apply the regs and they are open to interpretation. If you use the tables and regs as we have both stated there can be no arguement.

 

[rattlehead85]

Please elaborate on the difference between tn-c-s and a PME to clarify your point on this matter.

 

[1983]

I always belived main earth had to go direct to intake seen as the main gas and water has been bonded in 10mm from main in take met I wasn't sure if I could just get the 10mm required from the gas or water bond and take that to the ccu met to make it 16mm I like to be sure before I do anything

Why does it have to go directly to the intake?

 

[rattlehead85]

I always belived main earth had to go direct to intake seen as the main gas and water has been bonded in 10mm from main in take met I wasn't sure if I could just get the 10mm required from the gas or water bond and take that to the ccu met to make it 16mm I like to be sure before I do anything

A conductor can be used as a combined earthing and bonding conductor if it is adequately sized...........(awaiting to be pulled up on this now by certain people!!)

 

[davesparks]

I always belived main earth had to go direct to intake seen as the main gas and water has been bonded in 10mm from main in take met I wasn't sure if I could just get the 10mm required from the gas or water bond and take that to the ccu met to make it 16mm I like to be sure before I do anything

Without seeing exactly what you are talking about its hard to know.

Is you boss talking about running a bond from an existing earth marshalling bar, rather than running back to the MET? Or is it that he means to somehow join onto an existing main bond?

 

[davesparks]

Please elaborate on the difference between tn-c-s and a PME to clarify your point on this matter.

A PME supply is a TNCS supply which has N-E links made at specified distances along and at each end of the main distribution cable and at points near to the end of all service cables over a certain length. Distances will depend on each DNO and their individual requirements.
A lot of older TNS underground services are getting repaired and altered with CNE cables and N-E links being made at random points making then TNCS services but not necessarily being PME.
Then there are PNB services and services from dedicated transformers, TNCS supplies which are not PME and not subject to the dangers of PME.

 

[Simonslimline]

Please elaborate on the difference between tn-c-s and a PME to clarify your point on this matter.

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