Discuss 3 Phase supply calcs. in the Commercial Electrical Advice area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

dlt27

-
Reaction score
26
Hi and thanks in advance,
I have been asked to provide a new supply for a factory unit. They want supplies to welding bays, metal cutting saws etc. The only info I have been given is that they want a 250A(3 phase) supply from existing 600A panel (PME) to a sub panel and then from sub panel a supply to compressor(runs at 70A per phase) and 1 x 63A supply to 1 small 3 phase board and 100A supply for welding 3 phase distribution board.
I wondered if anybody could give advice on calcs etc. for working cable sizes. At my old company it was all provided and I just had to install. Now I'm self employed I want to be 100% sure I'm doing it correctly. Obviously I know I need to take into account volt drop, max zs for 250A MCCB etc.
I have got a rough idea of what sizes I believe I need, however didn't want to show working as I didn't want to get shot down by more educated people than myself. I was going to run separate earthing conductor with SWA's to meet bonding requirements.
I am obviously not going to commence work until I am 100% sure of sizes. I have done calcs on apps etc, but would like to go through everything so understand for future.
I understand 2 phase welders need balancing across phases etc and max volt drop from 600A panel to lighting and power are 3 and 5%.
I totally understand if it is too time consuming for somebody to explain or go through it, however it will be greatly appreciated. Thanks again
 
80m for 250A supply to new panel, From new panel -15m for 63A DB, 30m for compressor, and 30m for 100A DB. Ze =0.05 Thanks
 
250A on tray on its own. 63A DB on tray on its own. 100A DB and compressor are buried in the ground in ducting then on tray together to final positions. Thanks
 
Hi - dlt27

It would help us greatly if you can show us your calcs and the cable sizes you end up with, we can then point out any errors or add further queries for you to answer or hopefully confirm they are correct. Its asking a little beyond our kind nature for us to do it all for you and provide the design although if any member wishes to then that's fine, if we can give us some idea here what you have come up and how then we are more than happy to help.

Things to consider -
- Discrimination between devices.
- What distribution system you wish to install be it a busbar setup or Powerboard.
- Will the installation require corrective measures for the welding equipment (Power Factor Correction).
- Bonding if your running into other factory units.
 
I will go through it and put it on here tomorrow.
I wanted someone to go through process rather than do exact calculation. Thanks

Appreciate that, just trying to make the thread more concise otherwise it becomes a lengthy question and answer thread, if your using MCCB's against final distribution mcb boards then for full discrimination you will probably need an upstream device covering it of 160amp, if I recall to cover this 160amp device you would need a 400amp for full discrim' ... who has specified the 250amp?
Can you just draft a little block sketch of the proposed submains and circuits so we can better visualise your set-up.
 
Quick smoke packet calculation if the Ze is 0.05 and the manufacturer gives a max Zs of 0.09 at 100% your design max Zs is 0.075ohms at 80% to allow for conductor operating temp. Over a distance of 80meters a 185mm CPC would bring you just in under this value by a gnats cock. 120mm 4 core SWA based on 250A and 80 meter run will give you a volt drop of approximately 6.6V.

Using 35mm SWA from this panel board for the 30 meter 100A supply to the 3phase DB will give you a calculated volt drop of around 8.8V added to the 6.6V that's 15.4V In reality the total volt drop is going to be under this as it wont be pulling full load current and at 250A the cable isn't at its maximum CCC so wont be at maximum conductor temp at which the figures are based. With a 25mm CPC that would give you a calculated Zs/Zdb of around 0.12ohms which should be under the max permitted for a 100A OCPD.

The above is rough and vague but should hopefully point you in the right direction for your own calcs.
 

Reply to 3 Phase supply calcs. in the Commercial Electrical Advice area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock