3ph Mot bay - advise much needed!!

[spark-ticus]

Hi all, I would like some advise on a job i am about to undertake, A large industrial unit being used as an mot garage with an incoming 3ph supply of 63A. The client has ramps and testing equipment which totals 97A (this is adding together the various A ratings printed on the motor plates of each piece of equipment) along with a ring final circuit and a good chunk of flourecent tubes this puts it at well over 100A. Im not sure of the diversity allowance on this kind of install but i know all machinery will not be used at the same time. I think Its going to be a case of having a bigger supply fitted but would like to know how to put the wheels in motion and how big i should/can go

Thanks in advance guys an gals

 

[snowhead]

97amp per phase?

 

[davesparks]

You need to make your own assessment of diversity for this installation.

How often will more than one ramp be operating at once?
What kit is there other than the ramps? And how often is it likely to be used?
I think its fair to assume there is going to be a compressor in there somewhere, but again that's going to be cycling on and off all day.

I'd be surprised if, based on what you've said so far, you need more than the 63A. But without all the information how could I say for sure?

 

[ayjay]

just install, if the supply is inadiquet the supply company will have to upgrade it

 

[davesparks]

just install, if the supply is inadiquet the supply company will have to upgrade it

That is a very unprofessional attitude and quite frankly awful advice.

 

[Plonker 3]

just install, if the supply is inadiquet the supply company will have to upgrade it

What do you think the customer would think if they were told that?

As for upgrading the supply, yes it's possible if needed, but the customer will have to pay for it. IRS not just done by the DNOs

 

[spark-ticus]

the 97A is across all 3ph not per Phase, there is a compressor in there which is on a 20A supply. The 97A is across all the equipment which is 6 ramps and a brake tester, the ramps will take a vehicle up for example and then be suspended there for a period of time while whatever task is carried out on vehicle, they are all hydraulic ramps so once stationary are not dragging any current, can't imagine any more than 3 ramps being operated at exactly the same time as there are only 3 members of staff!! In addition to these as i mentioned the 20A compressor, a ring final circuit with computers printer telephone and a brew room, 18 flour single tubes and very little else.
With regards to assessing my own diversity are there any guide lines in the regs to work to, e.g. in the osg there are guidelines on domestic kitchens with regards to ovens ect

cheers chaps

 

[spark-ticus]

You need to make your own assessment of diversity for this installation.

How often will more than one ramp be operating at once?
What kit is there other than the ramps? And how often is it likely to be used?
I think its fair to assume there is going to be a compressor in there somewhere, but again that's going to be cycling on and off all day.

I'd be surprised if, based on what you've said so far, you need more than the 63A. But without all the information how could I say for sure?

As i have 63A on EACH phase can i to some degree divide my 97A by 3 as it is shared across the 3 phases ?

Please excuse my ignorence, have not done much 3ph at all but am keen to learn and want to get it right

 

[davesparks]

Are any of these machines 3phase?

You need to balance the single phase loads across the three phases as far as possible.

 

[spark-ticus]

Are any of these machines 3phase?

You need to balance the single phase loads across the three phases as far as possible.

Yeah all of the machines are 3ph

 

[Darkwood]

Give us a breakdown of the loads ....Diversity on car ramps is massive as they never really run for more than a minute and hardly ever in unison ...

 

[davesparks]

Right, how did you calculate the 97A figure from them? Did you multiply each machines rated current by 3? Or did you just take the rated current of the 3ph machines and add it to the other single phase loads?

With respect I think you would be better off engaging the services of someone experienced with these things to work with you in this.

 

[spark-ticus]

Breakdown as follows;
5 ton ramp has 2 motors each @ 8.4A = 16.8A
2.5 ton ramp = 8.3A
2x 3 ton ramp @ 9.5A each = 19A
4 ton ramp = 8.7A
4 post ramp = 16A
brake tester = 26A

I have ascertained all these A values from the motor plates

 

[Engineer54]

Seeing as you have 6 ramps, one brake tester, a compressor, plus lighting and a bit of small socket power, and only 3 operatives (which doesn't quite make sense to me) the diversity is going to play a major factor with regards to defining the max demand of this MOT centre!! I bet you'll never see 63A or anywhere close under the present set-up!!

I would imagine the brake tester is going to draw the largest load, and that will only be for around 30 seconds or so per test....

 

[spark-ticus]

Brake tester is he largest at 26A, he is going to be testing all vehicles from little pencil sharpeners right upto 7.5 toners hence the wide variety of lifts i suppose. So do you think i am going to be ok with 63A then.?

Also do all of the conductors need to be sea or can i use appropriate sized flex.? will be using cable tray

 

[spark-ticus]

......sorry that was supposed to say "Do all of he conductors need to be SWA or can i use the appropriate sized flex.? I will be Using cable tray swell

 

[Lucien Nunes]

the 97A is across all 3ph not per Phase,

I have ascertained all these A values from the motor plates

As i have 63A on EACH phase can i to some degree divide my 97A by 3 as it is shared across the 3 phases ?

These don't hang together. The fact that you are looking at figures with all three phases added makes me think Davesparks is right and you should work through this project with someone experienced in machinery and motor installation, who can fill in some of the blanks and help consolidate your knowledge base regarding 3-phase theory etc. There may be other aspects to consider, such as permissible voltage drop when starting motors, which are difficult to advise on without being on the spot and having all the data.

Personally I bet the whole place would run off a 32A supply so long as the voltage doesn't sag too much when two people hit their up buttons while the third is taking a spin on the rolling road.

e2a:

Do all of he conductors need to be SWA or can i use the appropriate sized flex

Surely you would use whatever type of wiring system the circumstances require? CY, SY, MIMS, SWA, any or all might suit depending on a bazillion factors we can't tell from here...

 

[Simlec]

......sorry that was supposed to say "Do all of he conductors need to be SWA or can i use the appropriate sized flex.? I will be Using cable tray swell

This is going to be one well spec job this.. Flex supply's in a workshop.. Love it.
Save your self some pain and get a local electrical contractor in.

 

[ian.settle1]

With comments like you have made above you won't be here much longer.

From your previous questions it sounds as if you don't know what your doing as you are clearly out of your depth here.

 

[Knobhead]

I didn’t realise you could get banned for incompetence, what else has our OP done?

 

[GMES]

I didn’t realise you could get banned for incompetence, what else has our OP done?

I was just thinking the same tony, he must have got a bit naughty judging by Ian's comment in post 19

 

[Engineer54]

I didn’t realise you could get banned for incompetence, what else has our OP done?

You must have only just missed it Tony... Came back at Simlec with a barrage of abuse, ''strangely'' that post now looks as if it has disappeared. ..lol!!

 

[Knobhead]

Oh well, I’ll just have to find someone else to have a go at.

 

[davesparks]

......sorry that was supposed to say "Do all of he conductors need to be SWA or can i use the appropriate sized flex.? I will be Using cable tray swell

Is be looking at steel conduit/trunking for a start from scratch job like this.

But then I was taught to do a job properly to a high standard!

 

[Engineer54]

Is be looking at steel conduit/trunking for a start from scratch job like this.

But then I was taught to do a job properly to a high standard!

Agree, a metal containment system would in my opinion be a must in such an environment. Ideally underfloor to supply the ramps and brake testing rig.... Trouble is, most electricians these day's only consider SWA cable...

 

[davesparks]

Or Flex as it appears here!

Underfloor probably won't be economically possible in a rented industrial unit, but it is possible to feed most ramps from above (if you use a bit of common sense about where you make the drop)

 

[telectrix]

SWA with the drops on strut (and maybe tray) would be my preferred way

 

[camerabloke]

Wet string would be the ops

 

[snowhead]

Wet string would be the ops

Bit over the top that.
Could be wet Cotton thread.

 

[davesparks]

SWA with the drops on strut (and maybe tray) would be my preferred way

Why do you day SWA?

Steel pipe/trunking gives better mechanical protection, and is much easier to add to when the inevitable changes are needed down the line.