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#71461 - 10/29/06 01:14 PM Fluorescent Tubes  
Sixer  Offline
Joined: Aug 2005
Posts: 265
On 2 recent jobs of replacing high-output tubes while the fixture was still on, I was getting small shocks when I was installing the tubes in the sockets. I was only holding the glass and was not grounded. My question is: Is this a capacitive path through me while the tube is trying to fire? I've never had this happen before - both of these jobs involved replacing the tubes in an outdoor sign.


"Will it be cheaper if I drill the holes for you?"

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#71462 - 10/29/06 01:49 PM Re: Fluorescent Tubes  
Dnkldorf  Offline
Joined: Dec 2004
Posts: 1,064
nowhere usa
Are the ballasts grounded properly?

#71463 - 10/29/06 01:50 PM Re: Fluorescent Tubes  
Rewired  Offline
Joined: Jan 2006
Posts: 558
Hamilton, Ontario, Canada
Actually I have had that happen while replacing regular 4' T-8 lamps.
I wonder if this all has something to do with how fluorescent tubes must be within like 1/2" of GROUNDED metal to fire correct, and even why some of those U-bents have foil strips on them??


#71464 - 10/29/06 02:39 PM Re: Fluorescent Tubes  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Have you ever noticed ust how dust loves to collect on fluorescent tubes, as well as TV screens?

The operation of the lights generates some static electricity. I expect that you wer, in fact, grounded... and allowed the static to drain.

#71465 - 10/29/06 04:08 PM Re: Fluorescent Tubes  
RODALCO  Offline
Joined: Dec 2005
Posts: 854
Titirangi, Akld, New Zealand
I usually use leather gloves and wear safety glasses just in case the tube breaks.

The product of rotation, excitation and flux produces electricty.

#71466 - 10/29/06 04:54 PM Re: Fluorescent Tubes  
Sixer  Offline
Joined: Aug 2005
Posts: 265
Yes, the ballasts are grounded. For one of them, I was on a fiberglass ladder under a canopy and I was making sure that I wasn't grounded after I got the first couple of shocks, yet it still happened. It's bizzarre getting a shock when all you are doing is holding onto the glass tube.


"Will it be cheaper if I drill the holes for you?"

#71467 - 10/29/06 06:16 PM Re: Fluorescent Tubes  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Sixer, I once saw the outside of a rubber gas line act as a conductor. The 10.000V impulse ran along the coil wire, jumped a 1" gap, ran alon the surface of the hose....then grounded to the engine.

Static electricity has phenominal voltages. Many thing that we think of as "non conductive" will, in fact, carry current at such high voltages.

#71468 - 11/02/06 11:13 PM Re: Fluorescent Tubes  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
When a Discharge Lamp is brought into operation (initial Arc becomes a Plasma), a charge is placed on the Lamp's "Envelope" (the outermost part of a Lamp).
This charge is the result of the internal ionization of materials, which rapidly threw things from a steady state (prior to passing the precursive initiating Arc), into a different state.

Normally, this charge will drain off the Lamp, and allow the full Plasma to be achieved without impeding the start process - or if the start process is completed, the charge levels become low enough to not be noticed from someone touching a Lamp bare-handed.

This is very common with "Low Output" and Low Power Fluorescent Lamps, being very close to metallic items.

Most HID Lamps fall into this category too, mainly because they have their Arc Tubes enclosed by separate envelopes, so the charge simply drains off through the socket connection, into a larger metallic body (also I have no wish to touch any HID Lamps in operation!!!).

On the other hand (OTOH), Fluorescent Lamps having High Output classifications (like F40 T12 HO - an 800 ma High Output Lamp, or F96 T12 VHO - a 1500 ma Very High Output Lamp), will leave a much higher charge on the Lamps, and these charges may not always completely drain off to metallic items in close proximity of the Lamps - resulting in "EEEOWWW" from the person grabbing a Lamp bare-handed.

The phenomina taking place here is not an actual (or required) "Path To Ground" for the charge on the Lamp to "find", but the "ability" for charges on the Lamp to flow to "something" having a different charge (could be higher or lower in charge state).

This is the old statement: "Difference Of Potential"

In the case of the Lamp zapping, one would not need to be connected to the Earth, or any other Ground Bonded Metallic structure/equipment - one simply needs to have a different state of charge, and there will be "A Difference In Potential" - thus allowing charges to transfer (in hopes to become "Neutral" or "Ground State").

Sadly, the unwilling victim has never been asked to nullify the Potential Difference! [Linked Image]
Physics just assumes you are in full agreement, and never asks / says a thing!


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#71469 - 11/03/06 02:55 PM Re: Fluorescent Tubes  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,223
SI,New Zealand
I usually use leather gloves and wear safety glasses just in case the tube breaks.

Good call there, mate.
I learned that lesson when I first started my time as a sparky, removing an old T12 (series start) tube from a fitting.
As was common, the end cap that holds the pins had jammed in the lampholder and as I twisted it, I must have squeezed the tube, because it exploded into pieces.
I have had a scar on my left hand ever since that took years to heal properly.
I've worn gloves ever since that day, when working with fluoro tubes and as Ray stated, safety glasses.
Getting a shard of phosphorus coated glass in your eye would not be fun at all.
I'm glad that they don't use mercury in fluoro tubes anymore, but the risk is there with older tubes.
Be careful.

#71470 - 11/03/06 03:37 PM Re: Fluorescent Tubes  
Luketrician  Offline
Joined: Jul 2006
Posts: 272
Sale Creek, TN USA
Not to mention those old pcb filled ballasts too. Those old fluro fixtures are just one big health hazard.

Luke Clarke
Electrical Planner for TVA.

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