Supplementary Bonding Conductors

[OnOff]

Excuse my possible ignorance / gaps in knowledge, but Supplementary bonding conductors: Can they be TOO big? As in, other than cost etc is there a problem if this has been done in 16mm sq? Would an EICR etc pick up on this as a problem for instance? Appreciate that the bigger the CSA the lower the resistance to earth fault current etc. What am I thinking of? Sure it's something to do with bonding being incomplete elsewhere....................

 

[NozSpark]

No there's nothing wrong with too big, but you may hae problems terminating it in an accessory earth terminal

I'm assuming you are on about supplementary bonding and not equipotential bonding

 

[Sidewinder]

Certain "special locations" would require "oversized bonding" think sect 710, & ERB's and you'll get there!

So no it is not an issue & I would not pick this up on an EICR for it to be coded.

However, as Noz has pointed out, they must be correctly terminated.

Struggling?

Think reducing pins!

 

[tom1]

i always thought cables are like womens breast they can be too small but not to big

 

[Manator]

I often use 25mm and 16mm for bonding, the last submain I installed was 25mm three core armoured I used a core plus the armour as earth and bonded the gas and water in 16mm, the gas meter was only a meter away and the water about 3 meters away. On some installs I have had to install even bigger bonding like Sidewinder said in his above post.

 

[Sidewinder]

TBH I rarely use anything less than 16mm on any of the domestic work I do if it is a solitary G&Y end of.

The only smaller G&Y I use on these jobs is the cpc!

Remember however, rarely if ever on "most" even large supplies, even TN-C-S/PME would you need to go above a 50mm.

Manator, things are on the change too!

I'm getting my ERB, even though it is "in" a consumer unit, we are moving the spec slowly, but cost is a BIG issue...

 

[kme]

Two jobs back, I fitted a 50mm supp. bond; between a new DB, and the adjacent plumbing services ]

It could technically have been a 25mm; but I didn`t have any around - I did have an offcut of 50mm; so used that.

The only issue that could occur; under exceptional circumstances, would be causation of the PFC to rise above that safely breakable by the OCPDs.

For instance. A 400A(BS88) radial TPN busbar cct; with 36 no. two phase tap-offs installed; each tap-off having a 32A BS88 OCPD.

Each phase of a tap-off feeding a 3-way SP DB (so 72 DBs in total).

These DBs are (mostly) paired up in small enclosures, separating rooms. These enclosures also contain DHW, DCH, flow & return heating, all in copperwork.

4mm supp. bonds were required in all enlosures; running from the MET of each DB, across the 4 pipes, and back onto the other DB in the enclosure.

Now; each individual board used to have a PFC of approx 4.5 - 5.3 KA

but not any more........................

After installing so many bonds; the PFC has risen way above the 6KA rating of some breakers - (separate issue; but some breakers are only 1 or 2 KA anyway {old 3871})

So resolving one issue has caused another - which will have to be picked up on the NEXT inspection..........

(For info - measured Zs at origin = 70KA!!)

 

[Sidewinder]

^ Thing is KME, even though you have measured it at 70kA, I'm guessing Ph-Ph rather than Ph to ground, (?) this will never be realised at the incomer.

I'm guessing I know the job where you fitted the bonds.

Don't forget that the DNO is presenting to this install at LV, thus the PFC will be limited to 25kA Ph to ground by their network design.

Thus, the PFC further down the install will be reduced commensurately.

Also, I had a long debate about this last week with you know whom.

You may find that as long as there is back up protection then you're OK with the reduced PFC, however, if a breaker trips and the PFC is above its breaking capacity then it should be binned!!!

 

[kerching]

quote.........(For info - measured Zs at origin = 70KA!!)

I usually measure mine in ohms, but it has been a carp day so I may be missing the subtle nuances of this method!.............. :run

---------- Post Auto-Merged 1st May 2012 at 00:00 ---------- Previous post was made 30th April 2012 at 23:58 ----------

also I am watching a prog on Quest about making fluorescent tubes and also putting the gusset in tights...both subjects close to my heart.... :coat

 

[springcrocus]

i always thought cables are like womens breast they can be too small but not to big

I disagree. What you can't get in your mouth is wasted, anyway.

 

[SPECIAL LOCATION]

also I am watching a prog on Quest about making fluorescent tubes and also putting the gusset in tights...both subjects close to my heart.... :coat

Is that....

"How Do They Do That" ?

or something like that????