Here at National Power Corporation (NPC) we occasionally see custom orders that add rear-mounted receptacles. The Ferrups, 9PXM, and 9155 are in the category of solutions with this custom capability. But are rear mounted receptacles the best solution for your customer?
The benefits of rear mounted receptacles are:
- Ease of distribution: Power distribution via rear receptacles is plug and play. Either the loads are plugged directly into the UPS cabinet or the loads are plugged into ePDU’s which are fed by the UPS receptacles.
- Speed of deployment: With plug and play distribution, there can’t be any faster method of deployment.
- Lower installation costs: The other distribution option is to deploy wall mounted electrical panels or some sort of cabinet distribution which adds materials and installation labor costs to the project budget.
- Reduced use of wall space and floor space: To install a wall mounted or floor mounted electrical panel the site must have the necessary wall/floor space.
There is a disadvantage of rear mounted receptacles. This custom feature eliminates the option to utilize an external maintenance bypass panel (MBP). An external MBP provides a wraparound path for power which gives the user the ability to completely remove power to the UPS while maintaining power to the critical load. This capability allows the end user to perform two important functions without shutting down the loads:
- Replace the UPS after a catastrophic failure without removing power to the critical loads.
- Provide complete preventive maintenance which typically includes checking the torque on input/output wiring.
Utilizing an external MBP in a rear mounted distribution application would negate the advantages of the MBP since activating the MBP feature will remove the loads to the UPS and any loads plugged into the UPS.
The question becomes, “Are the advantages of an external MBP significant enough to overcome the additional costs for utilizing wall mounted distribution?” There is no clear answer as each site will differ, each customer’s needs will vary. The best approach may be to educate your customer and let them make the decision. Some of the topics of discussion to have with the customer would include:
- Available wall space and floor space: Rear-mounted receptacles have a smaller footprint. The wall-mounted panel or floor mounted cabinet affects both. Note that the National Electric Code requires 36” of clearance be maintained at all times in front of a wall mounted electrical panel so the wall mounted option does affect floor space.
- Time to deploy: Plug and play distribution is faster but remember to consider the longer lead times for ordering custom equipment compared to the standard equipment that could ship immediately.
- Budget: Material and installation costs are lower with the rear mounted distribution.
- Post sales service: More thorough preventive maintenance is allowed with the external MBP as well as quick reapplication of power after a catastrophic event and UPS replacement if necessary without interrupting loads.
- Nature of the critical load: Can loads be easily shut down? What is the financial impact should there be an outage where a bypass switch would reconnect power quickly to get systems up and running? How easy is it to schedule an outage should there be a UPS failure?
It is the opinion of NPC that all sites should have an external MBP when possible. The discussion for deploying a UPS should always include this device until conditions dictate that an internal MBP option will suffice or no bypass option is needed for the application.
If your customer is on the fence about whether or not an external MBP is required you can share with them this thought. In my 37 years in the UPS industry, I have yet to hear of a customer that regretted installing an external MBP, but I have heard many regret not installing such a device.
- By Lamar Britt, Director of Power Quality Sales