wiring through joists.

[malcolmsanford]

now i would work taht out in english. 4" joist, 1/8 of the depth = 1/2". who said imperial measurements were complicated?

Personally mate I would have gone 4" joist 4/32 = 8/16 but know what you mean

 

[telectrix]

ore even 8/64 ths

 

[dtec dave]

I'm not disputing any of this..I know it is totally impractical to cut a notch to 50mm deep. I was just trying to point out a confusion on page 59..fig 7.1 clearly states that a notch is a route for a cable to pass through it..above fig 59 it states that any cable passing through a joist should be 50mm from the top. So if we were to take this literally a notch should be 50mm deep, if they were to make this clearer there should be 2 diagrams. 1 showing cables passing through a joist i.e a hole and 1 showing dimensions of a notch. Anyone in agreement???

 

[SparkyDips]

stronger than the modern force grown kiln dried unddersized crap that is thrown in buildings today.

they didn't do too bad a job holding up boxes of boating magazines in a recently mentioned dwelling lol

 

[Andy78]

It tells you the maximum depth your notch can be in relation to your joist. If this is less than 50mm then it must satisfy the other stated requirements to comply. Simples.

 

[lauriehurman]

IMHO where you put the notches and holes is building regs,
Where you run cables is wiring regs.
Yesterday's cables are "selected and erected" to yesterday's wiring regs.
When you select and erect it has to be to BS7671:2011. In this case 522.6.100.
That means just because there's a convenient hole in the joist doesn't mean that you can use it for twin&earth, unless of course you fulfil one of the conditions for mechanical protection. I don't have sufficient wisdom to assert whether a notch plate is sufficient protection.
Interestingly the 50mm is from the top or bottom of the joist not the surface of the floor or ceiling, i.e. does not include the depth of the floorboard. Strange.

Laurie

 

[telectrix]

Interestingly the 50mm is from the top or bottom of the joist not the surface of the floor or ceiling, i.e. does not include the depth of the floorboard. Strange.


​that's to allow for 3" nails. bear in mind that the average wood butcher or wet-head will use whatever he has to hand when nailing boards.

 

[Richard Burns]

Interestingly the 50mm is from the top or bottom of the joist not the surface of the floor or ceiling, i.e. does not include the depth of the floorboard. Strange.
Laurie

Also means that it is not possible to put cables through joists in the mid level floor of a property with 4" joists!!

 

[Octopus]

Also means that it is not possible to put cables through joists in the mid level floor of a property with 4" joists!!

Excellent, that sounds like fun complying with.

How daft, old houses often have joists with more holes than Swiss cheese and they seem to stay up.

 

[telectrix]

How daft, old houses often have joists with more holes than Swiss cheese and they seem to stay up.

that's because they were built, not thrown up designs by pencil pushing bean counters.

 

[krishcanag]

I could not care less about BS7671, the first priority of any trade working on site is make sure that at the end of it he/she has not weakened the structure, stuff the regs, use what's there and inform the IET to issue a guideline of old houses with existing holes in joists (weakened joists). Holes in joists should never be allowed in the firstplace!! or should be thinker than required in the first place to conpensate for electricans and plumbers
KC