safe plate requirements?

[gottahugenoggin]

Hi
ive read,or heard somewhere that safe plates are required to be 3mm in thickness to proved adequate mechanical protection to cables passing through joists at a depth less than 50mm,is this true?
Everywhere you look they seem to be around 1-2mm max.

 

[telectrix]

2mm is quite adequate to prevent a nail being banged through the cable.

 

[Rockingit]

Haven't got a copy to hand to check, but I think that 3mm is in the BGB. 2mm medium steel plate might stop a nail, but won't stop a power tool putting a shelf up!

 

[gottahugenoggin]

ok thanks ive not got myself a BGB as yet,has it changed much from the red one?

 

[Rockingit]

No, was wrong. 522.6 doesn't specify a standard thickness, just that whatever is used has to stop penetration and be earthed.

 

[gottahugenoggin]

Thanks,sorry for all the questions but how would you earth it/them? will the earth wire itself have to mechanically protected as where it connects to the plate it will be less than 50mm in depth? It sounds easier to cover all the bases with rcd protection! ha ha

 

[Rockingit]

RCD protection is likely to be mandatory anyway for other reasons, but you also do have to remember the practical side of life: Just because there may be a means of preventing a penetration from killing someone, if it happens the cable/circuit is shafted and then won't (or shouldn't be made to) work, so what's the point in knowingly installing one in a vulnerable position to begin with? Mrs Jones is going to be really thankful that the picture nail she banged in is going to result in half her front room needing to be replastered............

 

[Plonker 3]

You can actually also get a twin and earth cable with a outer earthed metallic sheath which also complies.

 

[telectrix]

these safe plates were meant to protect the cable when it is notched in the top of a joist. an example of this is on a terraced house landing ( the 3ft x 3ft square at top of stairs) where the joists are only 3" top to bottom.

 

[gottahugenoggin]

thanks for the replys guys,its not something ive learnt anything about so far.So in theory it would be good practice to use mechanical protection where ever a cable is vulnerable despite the circuit being protected by rcd.For instance if i were to run a cable to a room using existing notches.I like that,good practice.
Im still confused to how you earth the plates? could someone explain to a noob,thanks

 

[telectrix]

Haven't got a copy to hand to check, but I think that 3mm is in the BGB. 2mm medium steel plate might stop a nail, but won't stop a power tool putting a shelf up!

have you tried drilling mild steel with a 6mm masonry bit. only a complete numpty would try and get through it.

 

[Plonker 3]

Im still confused to how you earth the plates? could someone explain to a noob,thanks

Yes simply run a adequately sized earth wire between each plate, crimp and bolt it too it and run it back to the MET.

 

[Rockingit]

Yes, agreed, but how many times do we find ourselves dealing with complete numpty DIYer's here on this forum??? I'm fully in the 'find another installation method' camp on this, and on the few occasions when it's happened to me on jobs I've tried hard to do something else instead, but sadly Darwin hasn't quite killed off all the idiots yet.

 

[telectrix]

well. if it wasn't for RCDs maybe we could have helped darwin kill off a few more.

 

[Engineer54]

Bet you have a job and a half getting floorboards back flush/level too, if using these metal protection plates on the joists!! ...lol!!!