Wireing for 200a 3ph and 400a 3ph service.

[JohnMc45]

Looking at some numbers for the electrical service for the factory we are opening and found something that strikes me as odd.  We got them to quote for both a 200a and 400a service. The 200a 3ph service seems to be four runs of CV 95mm/sq  and one run of THW 50mm/sq I assume L1,L2,L3,N and G plus the cable tray. On the quote for a 400a 3ph service they just doubled all the materials. This is what I find odd. Doubling conductors is generally  frowned upon in Code here. Is this normal for Thailand?  Would larger not be cheaper?

[maxpower]

Doubling cables from transformer to switch-gear is common in TH and not a problem if done correctly. There is often a cost saving from using 2x smaller cables because the smaller cable is manufactured in larger quantity and more readily available.

[Crossy]

10 hours ago, maxpower said:

Doubling cables from transformer to switch-gear is common in TH and not a problem if done correctly. There is often a cost saving from using 2x smaller cables because the smaller cable is manufactured in larger quantity and more readily available.

Yup, and smaller cables are less of a wrestle and have a smaller bending radius (go round corners better). Bangkok Cable 120mm² THW is about 19mm overall diameter whereas 240mm² is about 26mm OD.

 

You may also find two small cables end up with a slightly larger carrying capacity. For example 2 x 120mm² @ 345A = 690A (spaced on cable tray) but 1 x 240mm² in the same installation is rated at 535A.

 

Numbers from here http://www.bangkokcable.com/product/backoffice/file_upload/131004_1-450!750V 70C 60227 IEC 01 (THW).pdf

 

[Crossy]

12 hours ago, JohnMc45 said:

The 200a 3ph service seems to be four runs of CV 95mm/sq  and one run of THW 50mm/sq I assume L1,L2,L3,N and G plus the cable tray. On the quote for a 400a 3ph service they just doubled all the materials.

You could actually save a little coin by running 2 x 70mm² for the 400A service (still rated at 488A). Assuming they are quoting for copper, aluminium cable would need to be one size bigger.

 

[impulse]

While the 50mm2 for ground may meet code, you may want to discuss it with an electrical guy familiar with surge suppression and bad power quality to see if it may cause you problems with surges, spikes and other power quality problems.  Especially if you're not sure of the quality of the power you'll be getting (based on onsite surveys).

 

If you're just running motors and other bulletproof equipment, you may not even notice it.  But if you're running equipment sensitive to power quality, your ground should be at least as big as your 3 phases and you'll be well served by industrial grade TVSS's- properly applied.

 

But that goes way beyond the skillsets of most installers and into the bailiwick of power quality engineers. 

 

Edit:  I should also add that it's a school of thought that causes a lot of friction between power quality guys and installers.  But keep in mind the codes are there for safety- with ampacity limits based on the maximum heat rise in the cable.  They don't tell you whether you'll save money in the long term by going to bigger wire to reduce I2R power losses, or improve power quality.  That depends on the length of the cable runs and a lot of other factors.

 

[JohnMc45]

Most of are equipment I think is safe dumb motors and heating elements. The only stuff I would be concerned with is a SAF DC6 drive, KB 3hp and 1/4hp dc drives. There is also a handful of counters and temp controllers but they are all 100-240Vac so I would think they would be fine?     

 

Yes that could be a very up hill battle with some electricians. I know a number that think it is fine to undersize the neutral so can only imagine there thoughts on a full size Ground. 

[maxpower]

1 hour ago, JohnMc45 said:

Yes that could be a very up hill battle with some electricians. I know a number that think it is fine to undersize the neutral so can only imagine there thoughts on a full size Ground. 

There are many instances where the neutral size is reduced or even non existent.