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Topic Title: 3 Phase Install calcs
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Created On: 30 October 2013 09:36 PM
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 30 October 2013 09:36 PM
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Posts: 113
Joined: 25 July 2008

Just looking for some info, when weighing up adding an additional 3 phase db what calculation process do you guys go through regarding viability for adding the extra load? do many of you use electrical design software. For example i do alot of subby work and one job at a school was adding a 3 phase 200amp supply db to a stage area to supply 10 dimming packs each taking 20amp per phase. You have the main lv incomer supplying a 400 amp 18 way iline distribution board via a 4c 95mm from here there is 8 mccb's supplying various dbs around the site consisting of:
1 - 80a mccb
2 - 100a mccb
3 - 63a mccb
4 - 80a mccb
5 - 80a mccb
6 - 100a mccb
7 - 63a mccb
8 - 100a mccb

Now to me surely adding a 200 amp supply to this is too much, but was just wondering how you guys go about adding a new db and what process you go through regarding diversity and loadings. Thanks.
 30 October 2013 10:14 PM
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Joined: 15 May 2002

Look at what they actually consume - and what the stage consumes.

My guess is that their 400A supply is seldom, if ever asked to deliver more than 200A (per phase) so it probably does have 200A spare

Also a 1kW lamp is quite a beastie and a 200A supply to the stage can power 150 of them! Find out how many lights they could ever imagine buying and double it. Then use that as your load.
 31 October 2013 08:41 AM
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Joined: 07 August 2007

If the electricity meter is a modern type, it should record the maximum demand of the existing installation, which is a good guide as to whether or not more load can be added.

Stage lighting does tend to grow up to about 110% of the available power to the stage area though.

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