diversity

[gavin.sibley]

Hi all was wondering if you could clear something up for me.

Have a meeting with an electrical designer in the morning for a project I'm working on, I'm not involved in the electrical side as such just been asked to go along as another input/person around the table. My question is as follows:-

We have a 60 amp three phase supply coming into our building, whic is a sub main run from the landlords main LV switch room. Off our board will be run a number of other sub mains into other parts of our building.


The question is, if we were to have a short circuit somewhere in the system, what would the likelihood be of us losing complete power to our whole building? I.E are we likely to get a problem with the landlords 60 amp submain breaker tripping out and killing all of our power should we have a fault? The reason I ask is that it came up in conversation today and the business is 100% reliant on having 100% uptime as far as power goes, and we do not have access to the landlords LV switch room, and there callout time to let us in would be atleast a few hours.

Many thanks for your thoughts,
Gavin

 

[GLENNSPARK]

well...you would need to look and consider carefully the time/current curves for protective devices...and plan accordingly...

different device characteristics have different time/current curves....

its not about the I N...its the curves....

 

[gavin.sibley]

Ok that's great, just looking for things to throw at the designer tomorrow as he's only on site once and the electricity supply is a major stumbling block at the moment, my biggest concern was the contractor wants to run a 40amp supply from our main sub board into our comms room, now without doing the calculations and just going from what I've heard/seen, there wouldn't be enough of a difference between that 40amp breaker and the 60 amp up stream to provide us with a good enough means of cutout, if that makes sense

 

[GLENNSPARK]

Ok that's great, just looking for things to throw at the designer tomorrow as he's only on site once and the electricity supply is a major stumbling block at the moment, my biggest concern was the contractor wants to run a 40amp supply from our main sub board into our comms room, now without doing the calculations and just going from what I've heard/seen, there wouldn't be enough of a difference between that 40amp breaker and the 60 amp up stream to provide us with a good enough means of cutout, if that makes sense

then you need to make sure the characteristics of the 60A breaker offer favourable discrimination over the 40A breaker...

 

[Engineer54]

Let the Electrical Engineer/designer make all of those decisions, that's what he's being paid the big bucks for!! Just officially raise any concerns you may have, so that he is aware and can give you an answer either there and then, or later when installation/construction drawings are sent to site,,,