Computer equipment load calculations

[vanetten]

I have a client who wants me to design electrical feeders and overcurrent protection devices based on 40% of maximum loads. Is this bad design practice? Should the design be based on maximum loads and not predicted operating loads?

 

[rr]

Should the design be based on maximum loads and not predicted operating loads?

It sounds like your comparing "Connected Load" with "Demand Load".

I never size anything with a "predicted" demand load. There are just too many variables that could happen.

 

[vanetten]

The client is giving me a operating load, max. The equipment has max or full load specifications. They are telling us to size feeders and ocpd's according to the max operating load. What do you design to?

 

[tlaidman]

I design to the manufacturers specs. If you don't and something goes wrong the customer will contact the manufacturer and he will say you did not install as to our spec. then your ass is in the ringer.

 

[rr]

The client is giving me a operating load, max. The equipment has max or full load specifications. They are telling us to size feeders and ocpd's according to the max operating load. What do you design to?

I never let clients tell me how to do my Electrical design. If your client insists on this type of design and you're not comfortable with it, ask for it in writing. That way, when breakers start to have nuisance trips 12 weeks down the road, you'll have paperwork to back up your design.

 

[tallgirl]

I never let clients tell me how to do my Electrical design. If your client insists on this type of design and you're not comfortable with it, ask for it in writing. That way, when breakers start to have nuisance trips 12 weeks down the road, you'll have paperwork to back up your design.

Also, ask them to explain why they think this is appropriate in writing. They might be working with assumptions that don't work under all possible circumstances. For example, a lot of equipment I see these days comes with dual power supplies and your customer might have this notion that they only need to size things half as big as if all the equipment was connected to a single phase or whatever. Well, if a breaker trips, the entire load is going to be instantly dumped onto another circuit, which could trip in turn, and depending on how the loads are divvied up, the entire room could come crashing down.