Unbonded Sprinkler Risers

[glennc@asttn.com]

I have beenresearching some issues we have been having with Transient Electrical Discharge(LightningStrikes) on somecustomer sites causing damage to fire alarm systems. Per code, at time ofinstallation we have installed Ditek surge suppressors on all Fire control anddetection loops as the enter and exit the building.

760.32 Fire Alarm Circuits Extending Beyond One Building.
Power-limited fire alarm circuits that extend beyond one building and run outdoors either shall meet the installation requirements of Parts II, III, and IV of Article 800 or shall meet the installation requirements of Part I of Article 300. Non?power-limited fire alarm circuits that extend beyond one building and run outdoors shall meet the installation requirements of Part I of Article 300 and the applicable sections of Part I of Article 225.

These surge suppressorsare grounded with 8 foot ground rods and are attached to the ground rodswith #8 solid copper wire. We were stillloosing equipment to TED?s.

At this point I brought in a consultant from DITEK, Chris Ralston and he involved the DITEK engineering department. Through video chat and pictures, each problem site was reviewed for installation to their standards. No discrepancies could be found. Yet, we were still experiencing TED?s and each time none of the surge suppressors had tripped.

At that point over the next two months the engineers began looking at ways to ?beef up? the system. We started with the system at Paddock Ridge Apartments. On Friday August 9^th, 2013, per suggestion of the DITEK engineers, I removed the Zinc grounding rods and replaced them with 8 foot copper grounding rods. I also extended any and all signal line circuit lines to be greater than 6 feet in length from the surge protector. This job was completed by the evening of the 9^th.

On the 11^th I received a call from *** and *** that there had been a storm and that the fire system had been ?knocked out.? I responded to the site and replaced the bad equipment, checked the surge protectors (again, none were triggered), and tested the system. The system was in the ?Normal? state upon leaving. I had not gotten down the road 3 miles when *** called me to return, saying that they had another lightning strike. I returned to ****** and found, once again, remote equipment damaged but no surge protectors triggered.

After replacing the bad modules once more I was leaning back against the closet door frame with my arm leaning on the sprinkler riser and tapping the wall with my screw driver trying to figure out what I/we were missing that would keep causing this problem. Just then, another wave of storms passed by, and I saw a flash out of the corner of my eye. All of a sudden I felt a mild electrical jolt between my elbow and the screwdriver touching the back wall. I had been ?bitten? from a discharge from the sprinkler riser. Upon examination, I found that the riser was not bonded/grounded to the buildings? electrical system. I looked over at the module I had just replaced, and it was shorted again. The transient electrical discharge was not coming in through the signal line circuit but seemed to be following the path of least resistance which appeared to be through the un-bonded sprinkler stand pipe.

According to NFPA 70 National Electrical Code 250.104, the sprinkler pipes must be bonded to the buildings? common electrical ground in a visible location on the stand pipe.

To verify this, I contacted **** Engineering and the engineers at **** and **(***) Engineering. Each entity pointed out that the possible differential in potential of an unbounded pipe/sprinkler riser could have fatal results. This was also verified by a licensed Master Electrician.

My question to you,is: Is it possible or probable that Transient Electrical Discharge (LightningStrikes) can be conducted through the un-bonded sprinkler riser and betransferred to the fire equipment through its connected wire and metal conduit.

The other question put forth to my company by the general contractor is what do they need to do to fix it? There are approximatly 14 sites with 6-11 buildings on each site. Each system is either metal out of the slab to manifold to residential PVC. or PVC from slab to metal riser to PVC. We advised were not electricians but we would be happy to check into it for them.
Would appriciate any help on this matter.

Glenn

 

[augie47]

Here are some previous threads that discussed the topic.
They may or may not be useful.
Someone may clarify, but I find the topic a but confusing.


It seems clear that you can not use the sprinkler pipe" for grounding purposes."
To me, it is less clear if you can/should bond it since if you do bond it and it is in contact wit h the earth it will become a grounding electrode.

This post and references will probably not help answer your question but should further the conversation.


http://forums.mikeholt.com/showthread.php?t=132384&highlight=bonding+sprinkler+piping

http://forums.mikeholt.com/showthread.php?t=148256&highlight=bonding+sprinkler+piping

http://forums.mikeholt.com/showthread.php?t=148256&highlight=bonding+sprinkler+piping

 

[GoldDigger]

Even though the riser cannot be used as a ground, or directly connected to any alarm wiring, its proximity to alarm equipment, including possibly sensors and actuators, makes it a prime source of harmful voltages and currents.
I would have an additional concern about induced potential differences from one end of the riser to the other end.
Even after the riser is bonded at the end nearest the alarm panel, it may still have necessary to add surge suppression on the internal wires before they enter the panel.

 

[gadfly56]

No question that the riser should be bonded to the electrical grounding system. The purpose is NOT to provide a ground as say, a water pipe would, but to prevent a fatality should the sprinkler grid become energized. This can lead to the strange situation where the sprinkler pipe and domestic water run next to each other and you can use one as a ground but not the other, even though they may connect back in the sprinkler riser room!

Now a more delicate question; what is the path from the sprinkler pipe to the modules/equipment? In compliance with NFPA 13, I'm sure no one is supporting any fire alarm wiring on the sprinkler pipe, right??hmy: