Wiring systems in office environment

[Alessandro]

Hello!
This is my first thread in this section of the forums. I'm relatively stuck with my design assignment, I was given drawings of a highways depot and I have to design the whole installation, show wiring systems, divide the installation into final circuits and do all the calcs. I'm okay with the purely theoretical part of the assignment, calculating things etc, but I have a problem with the initial part, where I have to show wiring systems on the drawings and explain the reason for my choices. The fact is that I have never installed something like this, and I don't know if what I have in mind can be done.


The building is divided into 2 sections, a workshop and the offices. "The office section is outer fairfaced brick with inner leaf blockwork. All inner walls are plaster finish. Ceilings are suspended 600 x 600 mm tiles on grid 2400 mm above finished floor level. Floors are carpet throughout with exception of the toilets, restroom and stores which have an anti-slip sealed covering."


So I have ground foor and first floor, power and lighting, 3-phase supply for the lift, one oven. My questions are:


1) Someone in college said to me that I should fix cable baskets on the wall inside the suspended ceiling area, and put all the cables there. Does this make sense? It sounds like you would spend thousands of pounds just to buy and install cable baskets, isn't this crazy?

2) Obviously the cable basket will have to go through walls. Can this be done without compromising the fire resistance integrity of the building? How? I can see how to do it with trunking, but not with baskets.

3) I was going to use PVC conduit in the offices to connect sockets and switches. How should I take the cables from the cable basket in the ceiling area to the PVC conduit? If I have the cable basket on one side of the room and I have to install a socket on the opposite side of the room, and the wall-to-wall distance is 4.5 metres, should I just lay the cable on top of the suspended ceiling for 4.5 metres or maybe clip the cable to the concrete ceiling? Or install cable baskets on the whole internal perimeter of the room just for one socket? But my teacher said I should not clip anything on the concrete ceiling or put the cables on the suspended ceiling, so....?

4) Should I put single core PVC insulated (not sheathed) cables directly on the baskets for power and lighting? Or do I need multi-core sheathed cables for better mechanical protection? But I'm sure it is better to have non sheathed single core cables for the PVC conduit, which is where all these cables are eventually going.

5) For the oven and the 3-phase lift supply, can I use multi-core PVC sheathed cables? Or SWA cables? Can I just lay them with the other cables on the basket?

6) When I do the lighting, I would probably go from one ceiling rose to the next rose directly, but then all the lighting cables would simply lay on top of the suspended ceiling. Do I have to clip the cables to something or should I leave the cables on the suspended ceiling?



How would you normally do all these things?

 

[davesparks]

What course are you doing and what sort of work have you been doing on site so far, and how long have you been doing it?

You appear to have been presented with a task which you haven't been suitably prepared for and I'm a little bit unsure about where to start with/how best to help you with it so a bit more background info about your xperience and knowledge so far would help.

Also whereabouts in the world are you?

 

[Alessandro]

Hello Dave, it's City & Guilds 2365, a design assignment. I don't even think they want us to go into such detail, but these questions came to me naturally. I'm prepared for the task, it's 7 questions mostly about design calculations using the information we have or information we can get from manufacturers of equipmment, then we find/calculate design current, ratings of protective devices, take account of inrush current if the load is inductive, using BS 7671 and OSG, diversity where applies, the usual stuff. The last exercise for the assignment is very easy, they give us a list of 5 types of cable and for each type, how many of them, and everything must go in a trunking. We must calculate a suitable size of trunking using the spacing factors in OSG. It's a very basic design assignment, it just takes time because the installation is quite large.
I'm only asking questions about the wiring systems part because I would like to do it realistically. If anyone can answer those questions it would be of great help!

 

[Pete999]

Hello!
This is my first thread in this section of the forums. I'm relatively stuck with my design assignment, I was given drawings of a highways depot and I have to design the whole installation, show wiring systems, divide the installation into final circuits and do all the calcs. I'm okay with the purely theoretical part of the assignment, calculating things etc, but I have a problem with the initial part, where I have to show wiring systems on the drawings and explain the reason for my choices. The fact is that I have never installed something like this, and I don't know if what I have in mind can be done.


The building is divided into 2 sections, a workshop and the offices. "The office section is outer fairfaced brick with inner leaf blockwork. All inner walls are plaster finish. Ceilings are suspended 600 x 600 mm tiles on grid 2400 mm above finished floor level. Floors are carpet throughout with exception of the toilets, restroom and stores which have an anti-slip sealed covering."


So I have ground foor and first floor, power and lighting, 3-phase supply for the lift, one oven. My questions are:


1) Someone in college said to me that I should fix cable baskets on the wall inside the suspended ceiling area, and put all the cables there. Does this make sense? It sounds like you would spend thousands of pounds just to buy and install cable baskets, isn't this crazy?

2) Obviously the cable basket will have to go through walls. Can this be done without compromising the fire resistance integrity of the building? How? I can see how to do it with trunking, but not with baskets.

3) I was going to use PVC conduit in the offices to connect sockets and switches. How should I take the cables from the cable basket in the ceiling area to the PVC conduit? If I have the cable basket on one side of the room and I have to install a socket on the opposite side of the room, and the wall-to-wall distance is 4.5 metres, should I just lay the cable on top of the suspended ceiling for 4.5 metres or maybe clip the cable to the concrete ceiling? Or install cable baskets on the whole internal perimeter of the room just for one socket? But my teacher said I should not clip anything on the concrete ceiling or put the cables on the suspended ceiling, so....?

4) Should I put single core PVC insulated (not sheathed) cables directly on the baskets for power and lighting? Or do I need multi-core sheathed cables for better mechanical protection? But I'm sure it is better to have non sheathed single core cables for the PVC conduit, which is where all these cables are eventually going.

5) For the oven and the 3-phase lift supply, can I use multi-core PVC sheathed cables? Or SWA cables? Can I just lay them with the other cables on the basket?

6) When I do the lighting, I would probably go from one ceiling rose to the next rose directly, but then all the lighting cables would simply lay on top of the suspended ceiling. Do I have to clip the cables to something or should I leave the cables on the suspended ceiling?



How would you normally do all these things?

1 Office power= 3 compartment trunking PVC Singles
2 Lighting PVC Conduit in void between slab and false ceiling PVC singles
3 Workshop power and lighting either busbar trunking for machine etc, lighting trunking for lighting, metal conduit and trunking for anything else in the workshop
4 Lift supply SWA
5Industrial cooker SWA

Hop this response is of use to you

 

[Alessandro]

1 Office power= 3 compartment trunking PVC Singles
2 Lighting PVC Conduit in void between slab and false ceiling PVC singles
3 Workshop power and lighting either busbar trunking for machine etc, lighting trunking for lighting, metal conduit and trunking for anything else in the workshop
4 Lift supply SWA
5Industrial cooker SWA

Hop this response is of use to you

Thank you Pete, very helpful. Just one question: when you say "slab", do you mean the ceiling above the false ceiling? So would you clip the PVC conduit on it?

 

[Pete999]

Thank you Pete, very helpful. Just one question: when you say "slab", do you mean the ceiling above the false ceiling? So would you clip the PVC conduit on it?

Yes and yes, just be aware of amendment 3 regarding exits etc, and try looking at Klik systems for lighting in suspended ceilings, I wont tell you it's for you to look for yourself as a trainee, if you get stuck I might be able to help only if you get stuck so have a root around with google for Klik and 7671 foe exit ways

 

[Leesparkykent]

A quick way to install conduit above the grid ceiling is to use threaded rod and conduit support spring clips.

 

[Alessandro]

Yes and yes, just be aware of amendment 3 regarding exits etc, and try looking at Klik systems for lighting in suspended ceilings, I wont tell you it's for you to look for yourself as a trainee, if you get stuck I might be able to help only if you get stuck so have a root around with google for Klik and 7671 foe exit ways

Thank you Pete, I will check Klik system and BS 7671 tomorrow. About Amendment 3, I'm pretty sure you mean not having cables and containment systems that can fall on you in the event of fires, but just in some areas, i.e. fire exits or passages that must remain clear in the event of fire. That's something they added with Amendment 3. Then obviously PVC conduit or fixing are not suitable, but I'll double check for suspended ceilings and wiring inside them. I'll definitely add this consideration to my assignment though, precious and vital advice.

And thank you Lee, will google that tomorrow. Time to go to bed now, good night guys.

 

[rolyberkin]

Thank you Pete, I will check Klik system and BS 7671 tomorrow. About Amendment 3, I'm pretty sure you mean not having cables and containment systems that can fall on you in the event of fires, but just in some areas, i.e. fire exits or passages that must remain clear in the event of fire. That's something they added with Amendment 3. Then obviously PVC conduit or fixing are not suitable, but I'll double check for suspended ceilings and wiring inside them. I'll definitely add this consideration to my assignment though, precious and vital advice.

And thank you Lee, will google that tomorrow. Time to go to bed now, good night guys.

All of your work and assignment needs to comply with BS 7671 (amendment 3) this is your bible, if you don't have a copy as well as a copy of the on site guide then I suggest you get one as you will struggle to complete your assignment and course without it. It is okay coming on here to ask the odd question you don't understand but you really need to be getting your head in the books, that is where your learning and understanding will come from.

Having recently bought both books it is like someone having switched the light on. I cannot understand why every college and training provider don't insist that every student has a copy?

With regards to the assignment they are looking for you to research wiring systems on the internet and via manufacturers data, give them a weblink or manufacturers name, I would suggest cable tray or baskets above the ceiling and something like dado trunking around the walls. Don't forget the CCTV, data, telephone and alarm cables inside! You will probably want different containment in the workshop area for mechanical damage. Don't forget the car wash area, outside lights etc etc.

 

[Alessandro]

All of your work and assignment needs to comply with BS 7671 (amendment 3) this is your bible, if you don't have a copy as well as a copy of the on site guide then I suggest you get one as you will struggle to complete your assignment and course without it. It is okay coming on here to ask the odd question you don't understand but you really need to be getting your head in the books, that is where your learning and understanding will come from.

Having recently bought both books it is like someone having switched the light on. I cannot understand why every college and training provider don't insist that every student has a copy?

With regards to the assignment they are looking for you to research wiring systems on the internet and via manufacturers data, give them a weblink or manufacturers name, I would suggest cable tray or baskets above the ceiling and something like dado trunking around the walls. Don't forget the CCTV, data, telephone and alarm cables inside! You will probably want different containment in the workshop area for mechanical damage. Don't forget the car wash area, outside lights etc etc.

I totally agree. I bought both BS 7671 and OSG months ago, and I've been telling my colleagues in college to buy both as soon as possible. And yes, not enough emphasis is being put on the importance of these books. At least C&G's textbook keeps constantly referring to BS 7671, you are supposed to understand that you have to buy it.

But it's almost as important to have other good textbooks that can clearly show how to use it, and where the important bits are. I love Installing Electrotechnical Systems & Equipment Books A and B, and Advanced Electrical Installation Work 8th Edition, and a couple more books for the practical and the science. The more you read about the same thing on different sources, the more you will get close to a 360 degrees understanding of the subject.

One question: with dado trunking, when there is a door but I need to continue the trunking after the door I was going to do something like this.



But it doesn't look very aesthetically pleasing to me. Is it normal to go around doors like this?

Second question: you said I should use tray or baskets above the suspended ceiling, which was the original idea. How would you go through the walls from one room to the next room with a system like this? I googled this for hours, maybe I should keep googling but maybe I can save some time and do something more useful.

 

[Pete999]

I totally agree. I bought both BS 7671 and OSG months ago, and I've been telling my colleagues in college to buy both as soon as possible. And yes, not enough emphasis is being put on the importance of these books. At least C&G's textbook keeps constantly referring to BS 7671, you are supposed to understand that you have to buy it.

But it's almost as important to have other good textbooks that can clearly show how to use it, and where the important bits are. I love Installing Electrotechnical Systems & Equipment Books A and B, and Advanced Electrical Installation Work 8th Edition, and a couple more books for the practical and the science. The more you read about the same thing on different sources, the more you will get close to a 360 degrees understanding of the subject.

One question: with dado trunking, when there is a door but I need to continue the trunking after the door I was going to do something like this.

View attachment 31486

But it doesn't look very aesthetically pleasing to me. Is it normal to go around doors like this?

Second question: you said I should use tray or baskets above the suspended ceiling, which was the original idea. How would you go through the walls from one room to the next room with a system like this? I googled this for hours, maybe I should keep googling but maybe I can save some time and do something more useful.

One way of doing it. If you have room over the door you can employ two more right angle bend and continue with the trunking, it gets a bit expensive to install, but to my mind accessibility and alterations are easy to make, add a socket etc

 

[Alessandro]

One way of doing it. If you have room over the door you can employ two more right angle bend and continue with the trunking, it gets a bit expensive to install, but to my mind accessibility and alterations are easy to make, add a socket etc

Thank you, accessibility and flexibility are my main concerns for this area.

I was looking at table 4A2 and I was surprised to see that there is no "Non-sheathed cables in conduit under masonry ceiling" installation method, the closest things are methods 4, 10 and 11. I'm almost sure it should be considered ref method B, even though it seems reasonable to assume that "higher than standard ambient temperatures may occur" (as in methods 21 and 22).

So I was thinking that I could use metal conduit for all the office lightings to allow for better dissipation of heat, and also to comply with the fire passages/exits requirements of Amendment 3. To be perfectly honest, most rooms, all the corridors and the stairways can all be classified as escape routes in the event of an emergency, and it seems to be quicker to simply use metal conduit everywhere. Some rooms are also passages that lead to other rooms, and one must go through them to exit the building. Steel fixings and conduit is needed pretty much everywhere.

 

[rolyberkin]

It has got to be a whole lot quicker, easier and cheaper to install tray than metal conduit everywhere, plus you then have the flexibility of additions in the future. Perhaps conduit in stairwells where it would be seen? If you go through a wall you only have to restore the integrity of the wall, using something like firestop ROCKWOOL® Multi-Cable Firestop

 

[davesparks]

It has got to be a whole lot quicker, easier and cheaper to install tray than metal conduit everywhere, plus you then have the flexibility of additions in the future. Perhaps conduit in stairwells where it would be seen? If you go through a wall you only have to restore the integrity of the wall, using something like firestop ROCKWOOL[emoji768] Multi-Cable Firestop

Quicker, easier and cheaper aren't necessarily the signs of a good quality approach to a design are they!

 

[rolyberkin]

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