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Power News LogoJuly 2012    

Why is it Imperative you have an

External Maintenance Bypass?

Have you ever asked yourself:

What happens if an upgrade is needed on your UPS and it must be turned off?

What happens to your load if you need to replace you’re UPS?

What happens if your UPS fails in the middle of the night and you need to get power back to your load?

In these situations and many others an external maintenance bypass can be invaluable. 

Note: from now on referred to as maintenance bypass

The Maintenance Bypass provides you with the capability of maintaining power to the critical load via ‘maintenance bypass’ while doing maintenance (and/or repair/replacement) on the UPS. All critical loads should have a maintenance bypass with personnel trained on its operation.

Although Maintenance Bypass’s come in many types depending on your power distribution set-up/needs; the most common being the 2 breaker. (See Image Below).

Maintenance Bypass Diagram

Note: The “maintenance bypass input” and the “bypass input” are from an identical source.

As you can see from the image the UPS output is tied to the system output via the “normally closed” maintenance isolations switch (or breaker). There is also a “normally open” maintenance bypass switch (or breaker) available for use. This way should anything happen to UPS you can supply your load directly via the maintenance bypass.


Although operating the maintenance bypass is straight forward it is imperative that your staff be trained on its proper operation. Before operating the maintenance bypass your UPS must be in internal bypass. Should the UPS be providing power via the inverter when the Maintenance Bypass is operated it could cause damage to your UPS and your load. Once the UPS is in internal bypass it is safe to close the maintenance bypass switch and open the maintenance isolation switch. In this configuration the critical load is being supplied via the maintenance bypass the UPS can be turned off and completely removed if needed without any interruption to your equipment.

Some common issues to keep in mind when operating your maintenance bypass

- When operating on maintenance bypass your load is not being protected by the UPS

This can be problematic especially when you have an unreliable utility. It is common to first transfer your load onto generator before going to maintenance bypass. This way you are relying on your generator not the utility

- Maintenance Bypass Miss-Operation – often leading to damaged equipment and dropped loads

Miss-Operation is always a potential issue, maintenance bypasses are available with mechanical and/or electromechanical safety devices which can be used to ensure correct operation.

As you can see from above the maintenance bypass is a very important part of your power path and should always be included in any new installations. It is also something that should be considered to be added if one does not already exist, and there is room (electrically and physically) to do so.  Some important questions you may want to know the answers to :

Do I have a Maintenance Bypass?

Do you know where it is?

Has my staff been trained on its proper operation recently?

Jantech is here to help you with these questions and any others you may have, find out more at our maintenance bypass selection, or give us a call today. 1-800-452-6832

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