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Rattling conduit #129111 08/02/04 10:47 PM
Joined: May 2003
Posts: 18
D
ds247 Offline OP
Member
When there is an overload, often just before the breaker trips the conduit will often start to rattle and shudder. Any one have an idea why? Just curious. Thanks

Tools for Electricians:
Re: Rattling conduit #129112 08/02/04 11:30 PM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline
Broom Pusher and
Member
That's the sound of the Conductors literally "Bouncing Around" inside the Conduit, from the high level of Fault Current + related magnetic forces.

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Rattling conduit #129113 08/03/04 01:53 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
Likely the conductors are trying to take the shape of a set of sine waves in the process. It can be a very memorable sound.

Re: Rattling conduit #129114 08/04/04 01:45 AM
Joined: Feb 2003
Posts: 939
F
frenchelectrican Offline
Member
also try use the jumper cable to start up large diesel engine also you can see the jumper cable do move even smaller jumper cable do move the same way with med/large gas engine too due the current and mangatic force on the wires to push each other out ward it happend to me many time espcally when the starter have direct short inside the starting motor [Linked Image]

merci, marc

ps it also do show up with 3 phase service too when someone is stupid egough to bunch each phase in one conduct and it will viberate and build up pretty good amout of heat too [Linked Image]


[This message has been edited by frenchelectrican (edited 08-04-2004).]


Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

Re: Rattling conduit #129115 08/04/04 06:22 PM
Joined: Apr 2001
Posts: 507
G
golf junkie Offline
Member
"It can be a very memorable sound."

It scares the H**l out of me!

Re: Rattling conduit #129116 08/04/04 10:31 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
Used to do work in a plant that had a pair of 500hp trailer-mounted screw compressors, served by an overhead 480V span. Motor starting would cause the three individual conductors to “repel“ each other.

Running, the three conductors hung in a vertical line, but during starting they would deform into an odd triangle. It looked quite weird.

If the overload occurs very often, periodic meggering to catch cable-insulation deterioration may be wise, partly depending on the cost of a related production outage.

Re: Rattling conduit #129117 08/07/04 01:18 AM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline
Broom Pusher and
Member
Glad Marc posted this:

Quote

also try use the jumper cable to start up large diesel engine also you can see the jumper cable do move

I once saw the very same thing occur - with of all things, the jump starting of one Diesel Electric Locomotive from another Diesel Electric Locomotive (this was at a Branch Line's Station where Locos are kept, fueled and light maintenence performed for equipment used as local switch duties).
The unit being "jumped" (an SW1500) was hard starting, which nearly drained the Batteries; so a running, warmed up unit (GP9) was used to jump start the switcher unit (the SW1500).

The cables bounced quite hard during locked rotor through the first few rotations of the Crankshaft, then they bounced accordingly as the "tighter" pistons / cylinders were moving up on compression.

Being that these Prime Movers are 2-stroke Diesels with Blowers (Superchargers) and Turbochargers, the cranking compression is lower, and compression increases when things move faster; - i.e. the scavanging devices kick in; but still has a large volume of air to squeeze into a small space during starting.

Wierdest stuff to see (and of course- no camera!). Jump Starting a Locomotive was, in lieu of a better word; "Odd Enough", but the reactions of the cables added more "!@#$%" and [Linked Image] to that Day's event!

p.s. since Marc has/does Engineer Locomotives (operates them), I suspect the scenario above is where His reply is targeted towards.

Also, as Scott ("Bjarney") replied, hard starting / large Motor starting does unique things to stationary Conductors - and their reactions are heard with a very "Distinctful Sound" when the Conductors are in Conduit.

Hydro-Pneumatic Plunger type Elevators (actually their Pump Motors) normally set things in motion when they are thrown across the line (started / turned on / begin doing something Kinetic, rather than occupying space and their Rotor has 100% Static Inertia situation...).
Conduits, Boxes, Strapping, Conductors - along with Panelboards, bussing and OCPD belch out a harsh "Buzz/Shake" for about 100-250 milli seconds.

Scott 35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Rattling conduit #129118 08/17/04 02:26 AM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline
Broom Pusher and
Member
ds247;

Quote

When there is an overload, often just before the breaker trips the conduit will often start to rattle and shudder. Any one have an idea why? Just curious. Thanks

Just wanted to know if the replies so far have been sufficient to describe the "wazzup???" and the "whaddaheck???" involved, per your original question
(Did the replies answer the questions OK, or just make more questions)
[Linked Image]

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Rattling conduit #129119 08/23/04 04:37 AM
Joined: May 2004
Posts: 7
F
Frank Martino Offline
New Member
The last time I heard a conduit rattling was because there was a fault current passing on the conduit.

Re: Rattling conduit #129120 12/08/04 12:51 AM
Joined: Oct 2004
Posts: 803
mxslick Offline
Member
Wanted to bump this up and add that I've also heard some motor contactors/overload relays emit a high-pitched squeal during motor starting....

Many years ago I also saw pictures of destructive testing of industrial switchgear..copper buss as big as one's leg were distorted into odd shapes, insulating supports totally destroyed, and the test engineers were reportedly knocked out of their chairs in the bunker by the blast!!

The fault current in the test was over 2 MILLION amps!! Yikes!! (I think the voltage was 4Kv.)


Stupid should be painful.
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