The first says it's in regards to wiring systems near building surfaces and says protect via 3.9.4.4 if "50 mm from the surface of a wall, floor, ceiling or roof"
The second is under wall or roof lining and says protect via 3.9.4.4 "within 50 mm from the face of the supporting member to which the lining or roofing material is attached"
So one situation the 50mm is from the external surface and the other the 50mm is from the supporting member but what I don't understand is what's the difference in these situations? Anyone else notice this?
For example wouldn't both apply to a gib wall lining? Which one is the correct one to apply when deciding when to apply the protection methods required?
Cable Protection 50mm 3.9.4.2 vs 3.9.4.3.2
Cable Protection 50mm 3.9.4.2 vs 3.9.4.3.2
Doug's correct that the headings help understanding.
3.9.4.2 "near building surfaces" relates to
(a) "concealed" wiring within 50 mm of the finished wall / ceiling / floor surface (ie outer surface); and imposes the 50 mm depth rule.
If no lining, then not concealed, so doesn't apply.
Also limited to(b) wiring not close to (> 150 mm from) corners.
If the cables to which the rule can apply either are min 50 mm from exterior surface of wall / floor / ceiling / roof, or are free to move to that depth, then NFA needed
But if are not, & can't move to, min 50 mm; then additional protection is required using any of the 3 methods in 3.9.4.4.
Those methods include 30 mA RCD; which takes care of most but not all domestic wiring.
Note the inclusion of "roof" in the list, as it affects wiring for PV arrays
3.9.4.3 " "under wall lining / roofing", being a separate clause, applies separately - and in some cases both may apply at same time.
Note no mention of ceilings or floors for this one.
It comes in 2 parts, and 3.9.4.3.1 isn't about protection, it simply forbids putting the cable in the listed place.
IE you're not allowed to run cables between the outer face of the purlins and the roofing material, as shown in Fig 3.6.
Doesn't matter how much protection you put in place, you're just not allowed to do it at all.
What you can do, provided the purlins are deep enough, is run cables through holes drilled in purlins, or using clips on the face of purlins.
If the cable isn't at least 50 mm from the outside face of the roof, then under 3.9.4.2; you have to have additional protection.
But what 3.9.4.3.2 does is move the measuring point from the outside face of the roofing to the outside face of the purlin (or whatever other structural item provides the "immediate support" for the roof.
How much difference this makes depends on how thick the roofing material(s) are.
Go to full post3.9.4.2 "near building surfaces" relates to
(a) "concealed" wiring within 50 mm of the finished wall / ceiling / floor surface (ie outer surface); and imposes the 50 mm depth rule.
If no lining, then not concealed, so doesn't apply.
Also limited to(b) wiring not close to (> 150 mm from) corners.
If the cables to which the rule can apply either are min 50 mm from exterior surface of wall / floor / ceiling / roof, or are free to move to that depth, then NFA needed
But if are not, & can't move to, min 50 mm; then additional protection is required using any of the 3 methods in 3.9.4.4.
Those methods include 30 mA RCD; which takes care of most but not all domestic wiring.
Note the inclusion of "roof" in the list, as it affects wiring for PV arrays
3.9.4.3 " "under wall lining / roofing", being a separate clause, applies separately - and in some cases both may apply at same time.
Note no mention of ceilings or floors for this one.
It comes in 2 parts, and 3.9.4.3.1 isn't about protection, it simply forbids putting the cable in the listed place.
IE you're not allowed to run cables between the outer face of the purlins and the roofing material, as shown in Fig 3.6.
Doesn't matter how much protection you put in place, you're just not allowed to do it at all.
What you can do, provided the purlins are deep enough, is run cables through holes drilled in purlins, or using clips on the face of purlins.
If the cable isn't at least 50 mm from the outside face of the roof, then under 3.9.4.2; you have to have additional protection.
But what 3.9.4.3.2 does is move the measuring point from the outside face of the roofing to the outside face of the purlin (or whatever other structural item provides the "immediate support" for the roof.
How much difference this makes depends on how thick the roofing material(s) are.
Re: Cable Protection 50mm 3.9.4.2 vs 3.9.4.3.2
The section titles:
3.9.4.2 Wiring systems near building surfaces.
3.9.4.3 Wiring systems under wall lining or roofing material
Give a clue to the differences
Then 3.9.4.3.1 has a better explanation, preempting 3.9.4.3.2
I think the key part of the wording is "through any space.."
Like acoustic wall lining battens for example.
So as is true in a lot of cases in the book, you have to read the whole section to get a full understanding.
3.9.4.2 Wiring systems near building surfaces.
3.9.4.3 Wiring systems under wall lining or roofing material
Give a clue to the differences
Then 3.9.4.3.1 has a better explanation, preempting 3.9.4.3.2
I think the key part of the wording is "through any space.."
Like acoustic wall lining battens for example.
So as is true in a lot of cases in the book, you have to read the whole section to get a full understanding.
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Re: Cable Protection 50mm 3.9.4.2 vs 3.9.4.3.2
Sorry, still not 100% in what the 2 different situations each clause are trying to get at
It's more 3.9.4.3 that's throwing me off
It's more 3.9.4.3 that's throwing me off
Last edited by JamieP on Thu Apr 23, 2020 1:42 pm, edited 1 time in total.
Re: Cable Protection 50mm 3.9.4.2 vs 3.9.4.3.2
Doug's correct that the headings help understanding.
3.9.4.2 "near building surfaces" relates to
(a) "concealed" wiring within 50 mm of the finished wall / ceiling / floor surface (ie outer surface); and imposes the 50 mm depth rule.
If no lining, then not concealed, so doesn't apply.
Also limited to(b) wiring not close to (> 150 mm from) corners.
If the cables to which the rule can apply either are min 50 mm from exterior surface of wall / floor / ceiling / roof, or are free to move to that depth, then NFA needed
But if are not, & can't move to, min 50 mm; then additional protection is required using any of the 3 methods in 3.9.4.4.
Those methods include 30 mA RCD; which takes care of most but not all domestic wiring.
Note the inclusion of "roof" in the list, as it affects wiring for PV arrays
3.9.4.3 " "under wall lining / roofing", being a separate clause, applies separately - and in some cases both may apply at same time.
Note no mention of ceilings or floors for this one.
It comes in 2 parts, and 3.9.4.3.1 isn't about protection, it simply forbids putting the cable in the listed place.
IE you're not allowed to run cables between the outer face of the purlins and the roofing material, as shown in Fig 3.6.
Doesn't matter how much protection you put in place, you're just not allowed to do it at all.
What you can do, provided the purlins are deep enough, is run cables through holes drilled in purlins, or using clips on the face of purlins.
If the cable isn't at least 50 mm from the outside face of the roof, then under 3.9.4.2; you have to have additional protection.
But what 3.9.4.3.2 does is move the measuring point from the outside face of the roofing to the outside face of the purlin (or whatever other structural item provides the "immediate support" for the roof.
How much difference this makes depends on how thick the roofing material(s) are.
3.9.4.2 "near building surfaces" relates to
(a) "concealed" wiring within 50 mm of the finished wall / ceiling / floor surface (ie outer surface); and imposes the 50 mm depth rule.
If no lining, then not concealed, so doesn't apply.
Also limited to(b) wiring not close to (> 150 mm from) corners.
If the cables to which the rule can apply either are min 50 mm from exterior surface of wall / floor / ceiling / roof, or are free to move to that depth, then NFA needed
But if are not, & can't move to, min 50 mm; then additional protection is required using any of the 3 methods in 3.9.4.4.
Those methods include 30 mA RCD; which takes care of most but not all domestic wiring.
Note the inclusion of "roof" in the list, as it affects wiring for PV arrays
3.9.4.3 " "under wall lining / roofing", being a separate clause, applies separately - and in some cases both may apply at same time.
Note no mention of ceilings or floors for this one.
It comes in 2 parts, and 3.9.4.3.1 isn't about protection, it simply forbids putting the cable in the listed place.
IE you're not allowed to run cables between the outer face of the purlins and the roofing material, as shown in Fig 3.6.
Doesn't matter how much protection you put in place, you're just not allowed to do it at all.
What you can do, provided the purlins are deep enough, is run cables through holes drilled in purlins, or using clips on the face of purlins.
If the cable isn't at least 50 mm from the outside face of the roof, then under 3.9.4.2; you have to have additional protection.
But what 3.9.4.3.2 does is move the measuring point from the outside face of the roofing to the outside face of the purlin (or whatever other structural item provides the "immediate support" for the roof.
How much difference this makes depends on how thick the roofing material(s) are.
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