Diversity calcs - need more copper my way, cant do the maths.....

[wade88]

Alright there lads,

Its been a little while since my last post ive been AWOL somewhat and been involved in other business. But now i have returned to the world of ball ache and once again, in need of some advice.

I hope you are all well. i need to spend some time over the next few days trying to catch back up on what ive missed, any gossip, re-read all Trev's jokes etc, note Tele how i have also completely given up on any attempts at correct grammar and spelling, so dont even bother,

Right, to the question.

Down here in Mordor, we have/will have run out of juice before the months up. We currently have a standard industrial supply, three phase in, 3 x 100amp fuses, away we go. But in the next month, i am expecting the delivery of several machines, that require a collective 198Kw. this is of course just the total sum of their spec plates, and until they are up and running, wont be able to gauge what they actaully draw under load, problem is, there is no way i will be able to get these suckers powered in without sending the building back to the dark ages.

So i have rung our DNO and requested another 3 phase line in, and they have sent me the forms with require total load figures of the existing system (absolute nightmare) and the potential new gear. i just dont know how i am going to give them these figures. As far as the current system is concerned however, i can have a crack at it with the standard div calcs for the basic stuff, lighting, rings, blah, but i dont know how to apply the div calcs to motors, and the remainder of the industrial machinery i have here. Should i just clamp the machines at what i percieve to be full load and use that figure as a base line for the sake of giving them some figures?

What a total mess of a question, i hope your following. its been a while since i have had to concern myself with issues regarding electricity, i have spent more time lately swinging hammers around...... :90:

All help, useless suggestions, maybe some useful ones and even abuse, is all welcome.

Hope your are all well lads and your all busy bees making some sweet honey,

Ben

 

[stef]

Hi mate, welcome back.
in your case you have to use the total rated demand of the machine spec. With production machines you can't really apply diversity as in worst case they are designed to run 24/7. I personally for a new install add 10% spare capacity cos there is always someone who wants something else here and over there.

 

[Knobhead]

198KW = 400V 285A @ unity PF. If we take the PF to 0.8 then we’re up to 342A this is assuming the machines are mainly motors.
Unless you can categorically say all the machines will not run together your looking at an additional 400A service head.
Good luck you’ll need it!

 

[wade88]

Stef mate dont even get me started on adding a few more things "here and there", its getting ridiculous. I dont know how many times i have tried to explain to the sales team who are perpetually selling more than we can manufacture then complaining its not getting made in time, then just suggesting throwing more money at new machines to deal with the forced work load, but failing to understand that THERE JUST ISN'T ENOUGH ELECTRICITY. i just get blank eye stares and "well cant you find a way to make them work Ben....?"

"oh well i am currently in the process of building a lighting harness in my garden shed you massive wassock ill bring it in next week"

"brilliant, i'll go ahead and process a further 20 tonnes of orders then!"

****s

merging sales staff with the practicalities of real life outside of targets and money is a recipe for violence. however.... moans aside, the DNO want exact demand figures for everything but i just cant see a way of providing that information (without spending hours at it). Would it be acceptable do you think to just break it down to say something like:

- lighting
- sockets
- HVAC
- motors
- production machines

etc.

B

 

[stef]

Sounds too familiar :cool3:

 

[Knobhead]

Sounds like a power analyser is called for here. Give them the actual maximum demand.

 

[telectrix]

do a scotty. tell them you can't possibly manage with 400A, you need 600A minimum.

 

[johnboy6083]

i would contact the manufacturers of the machines to find out the allowance for diversity. If there is any that is. There may be ways that you could stagger the starting of machines ect to reduce the load, ie if they run on a cycle for example.

bear in mind that a new supply by the DNO means extra switchgear, which may mean new switchrooms ect. It may also require the upgrading of any main bonding in the building.
This could turn out to a lot bigger job than you may be able to handle. If it gets top the point that your struggling to keep up, then there is no shame in admitting it to your boss, in fact he wopuld respect your honesty. However if you feel your upto it, then go for it.

I would by the electriciand design guide by the IET, and readit. I would also start to revise cable calcs, especially with motors ect. Allowing for frequent starting ect can increase the cable sizes.

good luck mate, and keep us posted.

 

[wade88]

I was hoping their engineers would give me the thumbs up or down on the bonding when they get in touch. Didnt really know how to approach that issue.

Extra switch gear isnt a problem once the meters are in i will just be putting in a single TP + N board anyway with 30+ ways just to cope with the over flow and mving some things around a bit. I think your right however with the machines, as a few have said already, not much can be done in regards to getting a decent div calc and if im honest i may have painted more of a horror story than i initially intended (always one for a little drama), the machines are form fill and seal machines with a few induction motors here and there but only the one over 15 horse power, the rest are only half a HP at most.

The existing system here isnt my concern in regards to power draw, we are probably at around 75% capacity, its the arrival of the new gear thats giving me the willies. All else fails, I will have to run a long leg from out end unit (first of three in a row, 5,500 sqf buildings) into our main manufacturing one, 30 meters away, take into account voltage drop and put a big boy in. Our end unit powers a single office, absolutely loads left on that, just dont like the idea of putting in such a heavy "temporary" cable with a lot of gear on the end of it. Seems a little counter productive.

 

[johnboy6083]

the main bonding size depends upon the earthing system of the supply.TNC-S means thaty your main bonding needs to be 1/2 the size of the coper equivelant of the suppliers neutral upto a max of 50mm.

TNS. the bonding size of TNs is half of the required earthing conductor. So the best way to keop this to a minimum size, is to work out the minimum size of earthing conductorfoir the mainsupply (or submain if supplying an outbuilding ect), and then half of that is the min size of you main bonding, with a max of 25mm2 and a min of 6.