ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

>> Home   >> Electrical-Photos   >> Classifieds   >> Subscribe to Newsletter   >> Store  
 

Photo of the Week:

100 Year old Lightbulb
100 Year old Bulb

Advertisement:-Left
Recent Gallery Topics:
What in Tarnation?
What in Tarnation?
by timmp, September 10
Plumber meets Electrician
Plumber meets Electrician
by timmp, September 10
Who's Online Now
0 members (), 163 guests, and 24 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Jan 2006
Posts: 47
N
Member
I am working under the assumption that DC circuits fall under the maximum 3% allowable voltage drop as stipulated by the NEC.


Is this correct?

It is for DC feeds to radio equipment located on the roof of a building being fed from rectifers in the basement.

Horizontal Ad
Joined: Mar 2005
Posts: 1,213
S
Member
NEC never actually requires 3%, just recommends it. I'd put this into the category of "it's always a good idea to oversize for voltage drop" though!

What's the acceptable DC voltage range of the equipment? If it can handle the drop, it's not a big deal.

Joined: Jan 2003
Posts: 4,391
I
Moderator
I agree with Steve, great idea to maintain less than 3% but not NEC required.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Apr 2002
Posts: 7,412
Likes: 7
Member
NJ:
This was a class 'discussion' item last nite.

Vd is a fpn (Fine Print Note), not 'Code' not mandatory.

Vd is a design issue, and could/may be debated via 110.3 (B)

'Good Practice' & 'Common Sense' are not in the NEC, but should be observed by all.

I would check the equipment for a voltage, and take a reading under load, if it's already installed. Or, I would do the calcs on paper beforehand, and 'lean' to a larger conductor.

John


John
Joined: Jan 2006
Posts: 47
N
Member
Thanks for the input,

Now that everyone mentions it I remember this coming up in past.

The equipment runs 48vdc and the equip manufacturer states that the equip is fully operational down to 36vdc and they often crank up the output on the DC rectifiers to compensate.

I will just have to come up with allowable voltage drop calcs for these designs based on that criteria.

Thanks for the help

Joined: Jan 2006
Posts: 47
N
Member
Just curious about others opinions,

Designing engineer for the clients wants us (the consulting engineers) to spec out pulling a Cat5e cable in the same 2" conduit with (6) #2AWG DC cables for the radio equipment.

This cable is simply an alarm cable that will tell them if the door on the Equipment cabinet is open or closed.

The cable pulls will be in the range of 200-400'.

Anyone have any tips for getting the Cat5 pulled in with the #2's without tearing it up


Joined: Jul 2004
Posts: 10,008
Likes: 37
G
Member
Back in the olden days when we were pulling fiber with other fat conductors in ducts we pulled it in innerduct, a smurf tube like deal. That may not be an option in 2" tho. You need to do a fill calc.


Greg Fretwell
Horizontal Ad
Joined: Mar 2005
Posts: 1,213
S
Member
I see smurf tube all the time to protect the fiber optic cabling, but yeah, not an option. Mil-spec cat5 has a stronger jacket and would easily hold up, but it's expensive.

Why not just pull the cat5e in last?

Joined: Nov 2000
Posts: 2,148
R
Member
If you have a couple of 90s, the Cat 5 is likely to be damaged or broken. We won't even install #14 control wires in with power wires larger than #4. This happens where there is a 90 near the end of the run. Some of the conductors will take the short path on the inside of the 90 and others will have to be a bit longer riding on the outside of the inner conductors. This extra length has to come from the feed end and if the Cat 5 is on the outside and if it can't slide by the other conductors it will stretch or break.
Don

Last edited by resqcapt19; 03/26/07 06:16 AM.

Link Copied to Clipboard
Advertisement:-Right


Tools for Electricians
Tools for Electricians
 

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC + Exam Prep Study Guides Now Available!
 

Member Spotlight
electure
electure
Fullerton, CA USA
Posts: 4,295
Joined: December 2000
Top Posters(30 Days)
Popular Topics(Views)
340,808 Are you busy
266,179 Re: Forum
247,119 Need opinion
New Page 2
Powered by UBB.threads™ PHP Forum Software 7.7.5