Purpose of the Drip Loop at SE - InspectionNews

Don Emerson · #1 (**permalink**) 11-06-2007, 06:31 PM

Today, in a discussion with a friend, it was stated that the purpose of a drip loop at the service entrance of the building is to prevent lightening from entering your building because "the lightening will not follow a loop." That's a new one on me. Anyone care to enlighten me on this subject??? If a bolt of immeasurable voltage were to be directed to a fixed point, would it not follow the wiring?

David Banks · #2 (**permalink**) 11-06-2007, 06:44 PM

Drip loop purpose is to prevent water that runs down the service drop from getting in the service mast and to the service panel.

Don Emerson · #3 (**permalink**) 11-06-2007, 06:52 PM

Thanks Dave. I guess the answer I was looking for was will a lightening strike follow a loop in a cable. My friend was an exec in a communications Dot Com and he swore his engineers told him that the cable was looped to prevent the strike from doing damage. Is there an understood rule in engineering that a massive voltage jolt will not follow a loop in an electrical cable.

Billy Stephens · #4 (**permalink**) 11-06-2007, 06:54 PM

Don,

A Drip Loop is just that. It's purpose is to keep water from running all the way down the Service line into the weather head

Lighting actually seeks it's discharge point from the negative charged ground and connects with that drawn point and completes the circuit. IE. tree,you,lighting rod, Before circuit is complete ,the positively charged leg is seeking multiple negative discharge points.The first one to complete the circuit causes discharge.

Billy Stephens · #5 (**permalink**) 11-06-2007, 07:10 PM

Quote:

Originally Posted by Don Emerson

My friend was an exec in a communications Dot Com and he swore his engineers told him that the cable was looped to prevent the strike from doing damage.

Don,

Your friend was the Butt of a joke as Engineers(not known for their humor) do have their own
way to say scram and are still yukking.

Gunnar Alquist · #6 (**permalink**) 11-06-2007, 07:22 PM

Don,

Seems to me that lightening is electricity and wires conduct electricity, looped or not. I would really like to see your friend provide some documentation.

I was under the impression that it was called a drip loop because it allows water to drip off of the SEC before the conductors enter the service mast. But, what the heck! Let's say lightning can't make turns. Works for me.

Actually, I agree with Billy. A number of years ago, a friend of mine had one of those potato clocks. If you remember, they worked on the galvanic reaction principle where two electrodes (one zinc and the other copper) are inserted into a salt solution and a small current is generated. Except in this case, you could use fruit or vegetables. Well, he had one potato and one apple. He explained to his colleagues that it worked due to the potential energy difference between the apple and the potato because apples grew in trees and potatoes grew in the ground. Apparently he hooked them good. And they were electrical engineers!

Michael Thomas · #7 (**permalink**) 11-06-2007, 07:43 PM

Actually the engineer is correct to this extent: lighting paths can be influenced by bends in a conductor.

For example changes of direction in down cables from lightning rods are minimized whenever possible and restricted to max 90 degrees at a given location and the cables entering a buildings from antenna towers are sometimes designed with a 90 bend at a building entry just above grade.

Billy Stephens · #8 (**permalink**) 11-06-2007, 08:25 PM

Quote:

Originally Posted by Michael Thomas

Actually the engineer is correct to this extent: lighting paths can be influenced by bends in a conductor.

For example changes of direction in down cables from lightning rods are minimized whenever possible and restricted to max 90 degrees at a given location and the cables entering a buildings from antenna towers are sometimes designed with a 90 bend at a building entry just above grade.

Michael,

The minimum angles facilitate a direct path to ground and reduces the chance a feeder discharge from connecting to one of the many drawn negatively charged possible discharge points.

The 90 bend is made in hopes of contacting one of those points instead of continuing its path to ground in the structure.

Jerry Peck · #9 (**permalink**) 11-06-2007, 09:00 PM

Lightning takes *ALL* paths, not just the easy ones.

The drip loop, however, is to allow water to "drip" off rather than to continued running down the conductor.

The only "drip" with lightning is that peed-in-your-pants feeling you get when you get too close to lightning and when it "drips" down to your shoes..

Jerry Peck · #10 (**permalink**) 11-06-2007, 09:03 PM

230.54 Overhead Service Locations.
- (F) Drip Loops. Drip loops shall be formed on individual conductors. To prevent the entrance of moisture, service-entrance conductors shall be connected to the service-drop conductors either (1) below the level of the service head or (2) below the level of the termination of the service-entrance cable sheath.
- (G) Arranged That Water Will Not Enter Service Raceway or Equipment. Service-drop conductors and service-entrance conductors shall be arranged so that water will not enter service raceway or equipment.

Billy Stephens · #11 (**permalink**) 11-06-2007, 09:56 PM

Quote:

Originally Posted by Don Emerson

If a bolt of immeasurable voltage were to be directed to a fixed point,

Don,

Lighting is very rarely a single bolt. I added some pictures above JPs post.
Some excellent studies have been done in Florida on Lightning.It has been known to melt Sand several inches in dia. and several feet deep.

Jerry Peck · #12 (**permalink**) 11-08-2007, 08:08 PM

Quote:

Originally Posted by Billy Stephens

Some excellent studies have been done in Florida on Lightning.It has been known to melt Sand several inches in dia. and several feet deep.

Many years ago I watched a show on scientists tracing lightning hits and following its paths through the sand, similar to what Billy said above.

They would treat it as an archaeological dig and painstakingly trace and follow the paths of the melted sand (now mostly glass trackings) and they would go any and every direction, branch out and join each other, branch out away from each other, and one lightning strike could generated traceable paths up to several hundred feet away from the strike area.

Really fascinating and let you know that lightning does not just affect 'the spot where it hits', but it affects a large area all around it.