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#195483 - 08/05/10 02:42 PM Motor fusing
Davo Offline
New Member

Registered: 03/21/10
Posts: 5
Loc: Toronto, Canada
I just got back from a booster pump re-and-re. The new pumps are 3 25 HP 575V pump assembly with control - each pump is labeled with a 22.2A draw. The engineer drawings are specifying that we are to supply 3-#6 to the 3-pump assembly fused with a 80A time delay fuse. Looking immediately at table 13 - an 80A fuse is too large for #6 T90. Yet then there is 28-200(d) in the CEC. Here is my question - given that you can up a fuse size to 225% of the motor FLC if it does not start, does the conductor size have to be increased accordingly? It does not mention this a far as I can see in the CEC.

I realize on the face of it, that it appears the engineer didn't consult the code - I would size the conductor normally (22.2 * 1.25) + 22.2 + 22.2. = cable #4. It appears that one motor is a backup only and may not be used at all unless another is manually disconnected.



Edited by Davo (08/05/10 02:49 PM)

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#195484 - 08/05/10 03:03 PM Re: Motor fusing [Re: Davo]
Davo Offline
New Member

Registered: 03/21/10
Posts: 5
Loc: Toronto, Canada
On a second look at the CEC all appears fine as long as only two motors are connected to operate at once - following 28-204(c) up to 300% of the conductor rating is permitted.

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#195516 - 08/07/10 11:21 PM Re: Motor fusing [Re: Davo]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8530
Loc: SI,New Zealand
Davo,
What sort of system is this if it supplies a 575V motor?
Just inquisitive there mate.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#195531 - 08/09/10 12:04 PM Re: Motor fusing [Re: Trumpy]
mikesh Offline
Member

Registered: 06/07/06
Posts: 614
Loc: Victoria, BC, Canada
I will reply to Trumpy first. 347/600 is the nominal system voltage. Very common in Canada and usually used where 277/480 is used in the US.
So to Davo 28-204 is the right rule and you are applying the right conditions. 125% if the largest motor with the FLC of each additional motor that must be able to run at the same time = wire size. The overcurrent rules allow a breaker as big as necessary provided it does not exceed %300 of the ampacity of the wire feeding the lot.
So 50 amp wire could have a breaker up to 150 amps. If you use #6 r90 then up to 190 amps, not 200. You probably have to start with a max of 100 amp breaker unless it trips, which lets you go up from there.

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