Conduit

[Albert]

In the OSG page 112 table 5D, we have recommended factors for using trunking.
what happens, or how the factor will be defined (to find the recommended diameter) if we have to run, (for example), 8m conduit with 3 bends, or could be 3m with 4 bends don't tell me that 3m with 4 bends is stupid , I'm looking for the principal. I had few answers but they did not sound very convincing.
Thanks, Albert

 

[Big_Spark]

Albert, the size of cinduit you run will be purely dependant on the number and size of cores to be run in it.

 

[Albert]

Albert, the size of cinduit you run will be purely dependant on the number and size of cores to be run in it.

Good morning, I thought it would be you...
If you look at table 5A page 110, it is very simple no long conduit and no bends, a certain cable size has a certain factor put them all together and it will lead you at the end to the total factor needed for this cable configuration, from this you find the suitable cable in table 5B. I hope that I passed this one.
Now when we have to run a longer cable (above 3m, straight run), we need to use table 5C, OK?
Now, (again), example to explain my question: want to run 6m conduit which will 'carry' 4 x 1mm2, 2 x 2.5mm2 and 2 x 4 mm2, with 1 bend.
1) 1mm2 factor is 16 = total 64
2) 2.5mm2 factor is 30 = total 60
3) 4mm2 factor is 43 = total 86
4) total factor needed is 210
5) table 5D (one bend) the nearest (above the total factor) is 233, meaning for this configuration the recommendation is to use minimum 20mm conduit.
I know that I can use the 40%/45% system but for that I need to find information concerning the cables 'space consumption' etc.
But if I would like to use this table (as it is already there), how would I calculate the same config. as above. but with three bends.

 

[Big_Spark]

Look on page 112, there is a table that gives you the figures you want..

 

[Albert]

Look on page 112, there is a table that gives you the figures you want..

Sorry to disappoint you, it does not give you the factor for 6m run and 3 or 4 bends, I could ask the same question concerning 8m and 3 or 4 bends. leave the programme and look @ the table 5D OSG page 112...

 

[Big_Spark]

Albert, the reason they are not there is because a run of that length would or should not normally have that many bends in it..according to the IEE anyway.

In the real world this is not always practical, so we need to use common sense and extrapolate from the tables the cable factor to use, if you have no other options

However, in reality you do what any decent spark would do and introduce draw in boxes, that way you break the run up. In practise you very rarely get a 6 meter long section, that has to bend around obstacles, that will not incorporate at least one draw in box.

These draw in boxes can be through, tee, right angle or rear entry conduit boxes.

 

[Albert]

Albert, the reason they are not there is because a run of that length would or should not normally have that many bends in it..according to the IEE anyway.
.

The explanation I had in class was that we take factor for 2 bends and add the factor for 1 bend, the meaning is that for the example question the total factor will be 233+333 = 566, this will be suggesting that using 32mm conduit will be reasonable. because this explanation did not look 'scientific' to me I asked this question. I know that if the conduit size is bigger you will be ok, but it is not always practical to use a bigger size conduit for financial and installation space, and at the end of the day where is the limit?. does the system of adding the bends factors make sense to you?, leave for a moment the practical side of it, I would like to understand the principal, if you remeber it.
In uni I had a prof. that called the safety factors, ' ignorance factors', the less you know the higher are the factors..., understanding gives you flexibility.

 

[Big_Spark]

Albert, I agree with your old professor.

The real problem is that many of the trainers today have no practical experience of the job, they are unable to "see" the problem.

Very few Sparks ever touch 32mm conduit, it is a real biitch to install and incredibly expensive, it is always cheaper, in every sense, to install 50x50mm trunking.

We had a apprentice last year that had a similar problem to you, and according to the calculations from his "lecturer" he would need to use 250x250 trunking to solve his problem. When we took a look for him we reduced it to 100x100 trunking, and even proved it using the regs..his "lecturer" complained we were interferring with his job...I won't tell you on a public forum what my partner told him about what he thought about his skills and ability to do his job!!

 

[Albert]

Albert, I agree with your old professor.

The real problem is that many of the trainers today have no practical experience of the job, they are unable to "see" the problem.

Very few Sparks ever touch 32mm conduit, it is a real biitch to install and incredibly expensive, it is always cheaper, in every sense, to install 50x50mm trunking.

We had a apprentice last year that had a similar problem to you, and according to the calculations from his "lecturer" he would need to use 250x250 trunking to solve his problem. When we took a look for him we reduced it to 100x100 trunking, and even proved it using the regs..his "lecturer" complained we were interferring with his job...I won't tell you on a public forum what my partner told him about what he thought about his skills and ability to do his job!!

unfortunately I have to agree with your partner... if they would be so good, would I need to waist your time? obviously I'm not an experienced Sparky, but commonsense will say that the bigger the conduit, the dipper you in the SH***
So if you know (I'm not sarcastic), could you tell me how you saved about (ruff figure) 50,000mm2 in csa...? sounds huge, basically what I'm trying to get is the answer to my original question, if you remember the process.

 

[Albert]

Albert, the reason they are not there is because a run of that length would or should not normally have that many bends in it..according to the IEE anyway.

In the real world this is not always practical, so we need to use common sense and extrapolate from the tables the cable factor to use, if you have no other options

However, in reality you do what any decent spark would do and introduce draw in boxes, that way you break the run up. In practise you very rarely get a 6 meter long section, that has to bend around obstacles, that will not incorporate at least one draw in box.

These draw in boxes can be through, tee, right angle or rear entry conduit boxes.

Just as I drove you mad with these I thought you will be interested to know that , I checked again today, no one had an answer, related to the table but your quoted reply came on finally, takes time to squeeze a lemon...

The other one was the question about the continuity test, maximum value of 0.5 ohm, although after your explanation I understand this subject I was interested to know the source of this value, so this value is a value that they use locally for this specific configuration in the workshop, they just forgot to mention it...