Wiring systems in office environment

[rolyberkin]

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

A quality approach has nothing to do with the consideration of these three factors. The job of a designer is to ensure compliance with legislation and regulations to achieve the given aims normally within a budget and time scale. We could all design gold standard or over engineered solutions and then sit at home all day as they are too expensive to implement or not required or necessary.

In this case the use of cable tray over metal conduit would in my opinion be quicker, easier and cheaper to install. I have not used the words inferior, you have implied this,it will in my view achieve the same results, cheaper with added benefits.

In my view any good design has to take account purpose, regulations, ease of fitting, anticipated installation time and material cost, all factors are relevant in the real world. In the given exercise (which I am also designing for my 2365) to put metal conduit under a suspended ceiling is not in my view the best option it would take longer to fit, cost more to both buy and fit and have maintenance and modification drawbacks over a cable tray or basket system. I know which I would rather fit, but of course only my opinion

 

[davesparks]

If it is purely a theoretical exercise for a C&G course then there is surely no need to go for quick, easy and cheap but would be better to design the installation in such a way that it demonstrates your design skills as much as possible.

 

[Alessandro]

Hey roly thanks for the input. I was going with metal conduit for lighting only because of the necessity to reach luminaires in the middle of the room, but if I can just use cable baskets or trays I can see the advantages. Like dave says, though, I would opt for the best possible design because what we are trying to achieve is an "ideal" installation. Would you fix trays directly on the masonry ceiling above the suspended ceiling? If my measurements are correct, there is a distance of about 295 mm between the top of the suspended ceiling and the masonry ceiling above it.



Looks like it could be done like this.

 

[davesparks]

How are the light fittings going to connect to the fixed wiring? Normally this would be achieved by rock roses, for which you would then have to fix besa boxes and gland whatever cables you are using into them. So by the time you've done that you might as well run conduit between the besa boxes and carry on with the tried and tested method

 

[Alessandro]

Is a rock rose something like a ceiling rose for suspended ceiling luminaires? Maybe made of metal?

I have a problem about current demand but it's not relevant with the topic of this thread. I was unsure if I should open a new thread.

So according to On-Site Guide, the current demand to be assumed for household cooking appliances is "the first 10 A of the rated current plus 30% of the remainder, plus 5 A if a socket outlet is incorporated". Now I have a problem understanding this.

If I have a 9.2 kW oven, 9200 W / 230 V = 40 A. So I should only consider 10 A + 0.3 * 30 A = 19 A. My current demand is 19 A, then I_n = 20 A, type B because it's a resistive load. But why? It's still a 9.2 kW, when it's operating at its full load of 9.2 kW it will be drawing 40 A, and the circuit breaker should invariably trip.

Maybe I'm missing something obvious...

 

[Alessandro]

Is a rock rose something like a ceiling rose for suspended ceiling luminaires? Maybe made of metal?

I have a problem about current demand but it's not relevant with the topic of this thread. I was unsure if I should open a new thread.

So according to On-Site Guide, the current demand to be assumed for household cooking appliances is "the first 10 A of the rated current plus 30% of the remainder, plus 5 A if a socket outlet is incorporated". Now I have a problem understanding this.

If I have a 9.2 kW oven, 9200 W / 230 V = 40 A. So I should only consider 10 A + 0.3 * 30 A = 19 A. My current demand is 19 A, then I_n = 20 A, type B because it's a resistive load. But why? It's still a 9.2 kW, when it's operating at its full load of 9.2 kW it will be drawing 40 A, and the circuit breaker should invariably trip.

Maybe I'm missing something obvious...

Unless they mean that, even if it's a type B circuit breaker that you use, it would still trip at 5 times the rated current for overloads, and even when it's drawing 40 A it would take too long for the bi-metal strip to bend and trip the mechanism. Food would be ready before it trips? So we assume, when we calculate this current demand, that we can "abuse" the bi-metal strip? But then what about the CSA of the cable, I would still be basing all my calculations on a current demand of 19 A.

 

[rolyberkin]

How are the light fittings going to connect to the fixed wiring? Normally this would be achieved by rock roses, for which you would then have to fix besa boxes and gland whatever cables you are using into them. So by the time you've done that you might as well run conduit between the besa boxes and carry on with the tried and tested method

Excuse my ignorance, what is a Rock Rose? The closest I can find online is an Ashley Rock, ceiling rose is that it? Can you not fix a ceiling rose direct to cable tray? I can see the advantage of doing everything in metal conduit. The task states to make reasonable assumptions which must be listed consistent with the most practical design solution and economic considerations. The answers only give you seven lines so I cannot see they want anything in too much detail!?

 

[Leesparkykent]

Excuse my ignorance, what is a Rock Rose? The closest I can find online is an Ashley Rock, ceiling rose is that it? Can you not fix a ceiling rose direct to cable tray? I can see the advantage of doing everything in metal conduit. The task states to make reasonable assumptions which must be listed consistent with the most practical design solution and economic considerations. The answers only give you seven lines so I cannot see they want anything in too much detail!?

A rock rose is the same as klik rose. Imo for the office wiring, depending on the layout it may be easier to have a run of suitably sized trunking from the board down the center of the office. From this trunking you could have tap offs of conduit coming off to supply klik roses that are terminated into through boxes and end boxes for the lighting. You could also have besa boxes bushed directly on to the trunking for the lights nearest to the trunking.

 

[rolyberkin]

A rock rose is the same as klik rose. Imo for the office wiring, depending on the layout it may be easier to have a run of suitably sized trunking from the board down the center of the office. From this trunking you could have tap offs of conduit coming off to supply klik roses that are terminated into through boxes and end boxes for the lighting. You could also have besa boxes bushed directly on to the trunking for the lights nearest to the trunking.

Thanks, there are about 2 x 3 tube luminaries per floor a central feed would work well due to the layout of the lights. All this discussion is spurring me on to get the final few units completed on my 2365 so I can get on with the NVQ conversion

 

[Leesparkykent]

Thanks, there are about 2 x 3 tube luminaries per floor a central feed would work well due to the layout of the lights. All this discussion is spurring me on to get the final few units completed on my 2365 so I can get on with the NVQ conversion

We done a big office last year, It was 3 floors in a U shape. On each floor the the U shape was split in to three sections which were open plan office space. Plant room on the ground floor with distribution circuits fed from mccb's to a board in each section on every floor. From each board we done exactly what I posted above for the lighting. For the floor box sockets which were sunk in to tiles of the raised floor access system we installed two bits of tray one for data the other for power for the floor box sockets. The floor box sockets were wired in 4mm nyy-j as a radial with a 4mm green and yellow back to the board from the last socket for high integrity earthing. Each circuit was arranged so that no more than 8 work stations/ computers was on each circuit due to earth leakage.

 

[davesparks]

Excuse my ignorance, what is a Rock Rose? The closest I can find online is an Ashley Rock, ceiling rose is that it? Can you not fix a ceiling rose direct to cable tray? I can see the advantage of doing everything in metal conduit. The task states to make reasonable assumptions which must be listed consistent with the most practical design solution and economic considerations. The answers only give you seven lines so I cannot see they want anything in too much detail!?

Rock rose is a plug in ceiling rose. No you can't mount it directly onto tray as they need to be fitted to a besa box as they have exposed terminals at the back, they are not the same as a surface mounted ceiling rose.

 

[Alessandro]

I can't believe how much can be learned in a convenience store. This place had everything, perfectly visible from every angle: large tray going around the shopfloor, smaller trays branching from the large one (one of these smaller trays ended at an air conditioning unit), PVC and metal conduit for lighting, fire alarm etc, something that looked like suspended PVC trunking with lighting just underneath it, and so on. The job was a little rough here and there though, I'm sure I could do a lot better than that.

 

[Alessandro]

I'm not sure how to design the CCTV circuit. Do I need a dedicated radial and a 3A circuit breaker? I just need very essential, basic information for this part of the assignment. Maybe I can use the outdoor SON-T lighting circuit for it instead of one whole dedicated circuit?