All maintenance prohibited by OSHA?

[ojfsdi]

I was just told that OSHA prohibits performing any maintenance on power distribution gear while it is under load or powered on.

Sounds patently insane to me.

What? Are we supposed to just build two or three separate data-centers and migrate all services out of one at a time so we can shut down the room-wide UPS to change a battery string?

I'd like to see a citation of the regulation at least before I buy that....  Show me one shop that refrains from adding circuits to breaker cabinets hot.  One.

[al_buffington]

Hi,

The standard in question is NFPA 70E, "Standard for Electrical Safety in the Workplace" . I cannot provide you with a copy of the document itself, however there are several resources available on the SE website which discuss it in detail:

https://www.se.com/us/en/product-range/64253-solutions-for-osha-and-nfpa-70e-compliance/#documents

You mention two different scenarios in your post:

1. Shutting down the room-wide UPS to change a battery string  

2. Adding circuits to breaker cabinets hot. 

These are very different. Typically, a data center UPS will be sold/installed with a maintenance bypass panel. This allows a UPS system to be powered off and  completely isolated from the utility for maintenance purposes (including changing batteries).

Regarding the installation of a branch circuit breaker in a PDU, many customers have dual-corded loads which would allow them to be powered from 2 different sources for redundancy and maintenance purposes. 

[ojfsdi]

okay.  I read through the page you linked to (the overview and documents).  It doesn't cite any specifics on why going to external bypass would be mandatory for common UPS maintenance.  That page really felt more like a sales funnel for SE's consulting services.  And seemed very general indeed, which isn't surprising as SE sells a lot more than UPSes.

I also obtained a full copy of NFPA-70E.  I downloaded every page of it with a quick program I wrote, but it's in PNG files because the NFPA doesn't want it to be readily searchable.  I won't share it here because of preposterous copyright restrictions on what is basically law by proxy but here's how to access it yourself:

1. Get login credentials at http://bugmenot.com/view/nfpa.org
2. click the free access button at https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?...

After browsing it for a few minutes myself, I don't think it has a section on UPSes at all.

What's the article or section of 70E that implies needing to go to external bypass and shut down a UPS fully before UPS maintenance?

I'll follow the code if I can find the specific applicable section.  But if such section exists, I find it kind of suspicious that UPSes would be 'typically' installed with an external bypass, as opposed to 'absolutely always'.  And kind of suspect that any UPS manufacturer knowingly includes the functionality of hot swapping modules or batteries when code forbids it.  It would sound like an extraordinary liability on the manufacturer's shoulders to me to knowingly facilitate a code violation.

P.S.:  This is not a feature request to wire the Symmetra cabinet door to the R.E.P.O. contacts internally.

[al_buffington]

Hi,

I don't believe there is a section specifically related to Uninterruptable Power Supplies in the NFPA 70e, however the standard still applies since it's talking about work involving electrical hazards. I believe this is discussed in section 130. The NFPA should be applied in conjunction with the requirements listed in the National Electric Code. Although its main theme is battery replacement, this article mentions many of the relevant sections of the NEC that would apply:

https://www.ul.com/news/uninterruptible-power-supply-ups-system-retrofittingreplacing-new-batteries

When the PX was launched in 2001 the hot swapping of most modules was permitted. In January of 2016, Schneider Electric revised its position on the hot swapping of modules in the Symmetra PX based on changes to NFPA 70e. As it relates to the PX  (or any UPS really) you must consider such factors as the available electrical energy at the supply to the UPS, and the proximity of the operator to the backplane connectors in the UPS (which would be exposed when a module is removed). Some modules within the PX40/80/100 can still be replaced or removed with the UPS in live operation (Intelligence Modules, Batteries, PSUs, various communication boards). The Power Modules and Static Switch can only be replaced while the UPS is either in maintenance bypass or off. As it relates to the external bypass, when I say "typically" I really mean almost always. If I were to wager I would say over 95% of installations have one - and even that may be understating it. We don't require one to be purchased, and some customers either don't want to spend the extra $ or have an application where it's not a big deal to shut down the load. 

[sbagdon]

i was going to say, we have (2) Symmetra solutions here... a single with a bypass switch for maintenance, and a double with no bypass switches (yet breakers) yet able to run the entire room with just 1 unut... we've swapped power and battery modules live on all the units, yet we've lost each ups at least once, and Schneider refues to work on the unit until we could demonstrate and measure that there was positive disconnect on the input load leads.

The UPS unit should be able to be removed from the circuit, either via bypass (and preferably a lock-out-tag-out padlock), or redundancy (which again would require lock-out-tag-out of the breaker-deenergized device).

The OP says "battery strings", so not sure if that is something with an Anderson plug, or some sort of battery tray/cabinet/room that would require a positive disconnect pre-work.

[ojfsdi]

"Schneider refuses to work on the unit until"

Wow.

If anyone should be competent and confident enough to safely work on energized equipment, I'd expect Schneider to have such necessary training and tools.  How disappointing.  I guess I won't be hiring them or investing in more of their gear any time soon.

It's entirely a hysterical, false dichotomy to say it's unsafe to work on something energized, and safe when it's de-energized.  I could trip on my shoelaces walking from the bypass to UPS and impale my skull on a screwdriver for instance.

If a live conductor is so dangerous, how dare we handle an energized c13 power cord, or disconnect a power strip from a wall without switching the breaker off first?  Indeed your slippery little fingers are much closer, 20-30 times closer, to energized conductors when disconnecting your personal massager from the wall in a dark bedroom, than when swapping a Symmetra power module.  Same voltage potential to ground too fwiw.  If the PX bus bars were running at 277 or honestly, in the 25kv range, I'd understand some paranoia.  But lets not forget the bus bars are visible in open air from the back of the unit with only a single sheet of perforated sheet metal to keep fingers out.

There is no substitute for common sense, ppe, due care, and good design.  Encouraging cold work as a substitute for any of those is a great way to injure the poor soul operating the bypass the day someone left a fault to ground in place when they closed up the UPS.  followed by a major outage.  You're not going to replace a damaged bypass without major downtime.  Oh wait. I can hear it now, get another bypass for the first bypass.  Give me a break.  Bypasses all the way down.  Untenable.

[al_buffington]

@ojfsdi As I stated previously, at the time of release of the Symmetra PX the replacement of power modules was permitted with the UPS online. Many years later, this became no longer an acceptable practice based on NFPA 70E. Whether or not a task can be performed live or not is dependent on the arc flash calculations for what you are working on. In the case of the Symmetra PX is is not allowed for certain tasks. It is not remotely the same as plugging a power strip into the wall or disconnecting one's phone from the AC. In some systems designed more recently, there are options for the live swap of modules.  As for operating the bypass breakers, this is considered safe when wearing the appropriate PPE. If there was damage to the bypass panel then yes it would require downtime to correct it. All Schneider FSRs are trained and adhere to NFPA, NEC, and OSHA standards for safety.  

Hi @sbagdon 

I believe you are referring to a single phase Symmetra. What you are saying about refusing to work on the unit would make sense under certain scenarios where the work would be unsafe,  but to my knowledge this does not include the replacing of most modules. As you have stated it's okay to replace the power modules and battery modules on these systems while its running.