Sanity check please Medium Voltage terms' - Page 2 - Electrician Talk - Professional Electrical Contractors Forum
CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Forum > General Electrical Discussion


Reply
 
Thread Tools Display Modes
Old 02-16-2015, 08:46 PM   #21
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Nova Scotia, Canada
Posts: 5,261
Rewards Points: 286
Default

Quote:
Originally Posted by Jhellwig View Post
That isn't talking about shields. It is talking about the amour on armoured cable.
Trust me when I tell you that the CEC is convoluted and hard to understand at the best of times.

That is why I outlined part 5 of rule 36-104 which specifically directs you to 10-304 part 2


From 36-104

(5) Subject to Rule 10-304, metal sheaths, shielding, armour, conduit, and fittings shall be bonded together

and connected to ground.


Rule 10-304 is in my previous post.


After 20+ yrs of experience I can tell you beyond a shadow of a doubt......we don't terminate both ends and the interpretation is that it is a code violation to do so.
In fact.....if I had the CEC handbook in a digital version, I remember the clarification for this rule and it specifically states that interpretation in there as well.
__________________
I want to get a job cleaning mirrors......its something I can see myself doing.
Rollie73 is offline   Reply With Quote
The Following User Says Thank You to Rollie73 For This Useful Post:
glen1971 (02-16-2015)
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Sponsored Links
Advertisement
 
Old 02-16-2015, 08:48 PM   #22
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Nova Scotia, Canada
Posts: 5,261
Rewards Points: 286
Default

Quote:
Originally Posted by Arc'n'Spark View Post
I have never seen, and certainly never installed, shielded MV cables without the shield grounded at both ends and at any splices or taps in between. As for stray current flowing on the shield - big deal. Most cables used today have shields rated as EGC's anyway (I still pull a separate ground, though). Would you not bond an enclosure with splices in it in a 600V system for fear that your ground wire might be inadvertently carrying stray current? As someone said earlier, if you have enough current flowing on the cable shield to damage the conductor insulation, you have big problems lurking somewhere.
Im not saying you're wrong.....or anyone else is wrong for that matter I'm just saying what is done in my neck of the woods and why we do it that way.
__________________
I want to get a job cleaning mirrors......its something I can see myself doing.
Rollie73 is offline   Reply With Quote
Old 02-16-2015, 08:51 PM   #23
Senior Member
 
Join Date: Jul 2011
Location: Pennsyltucky
Posts: 430
Rewards Points: 252
Default

Quote:
Originally Posted by Rollie73

Trust me when I tell you that the CEC is convoluted and hard to understand at the best of times.

That is why I outlined part 5 of rule 36-104 which specifically directs you to 10-304 part 2

From 36-104

(5) Subject to Rule 10-304, metal sheaths, shielding, armour, conduit, and fittings shall be bonded together

and connected to ground.

Rule 10-304 is in my previous post.

After 20+ yrs of experience I can tell you beyond a shadow of a doubt......we don't terminate both ends and the interpretation is that it is a code violation to do so.
In fact.....if I had the CEC handbook in a digital version, I remember the clarification for this rule and it specifically states that interpretation in there as well.
I appreciate you clarifying that and will take your word on the interpretation as you would certainly know more about the CEC than I. It seems strange to me that our codes, which seem to be generally pretty harmonious, would be at odds on something as commonplace as this.
Arc'n'Spark is offline   Reply With Quote
The Following User Says Thank You to Arc'n'Spark For This Useful Post:
Rollie73 (02-16-2015)
Sponsored Links
Advertisement
 
Old 02-16-2015, 08:58 PM   #24
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Nova Scotia, Canada
Posts: 5,261
Rewards Points: 286
Default

Quote:
Originally Posted by Arc'n'Spark View Post
I appreciate you clarifying that and will take your word on the interpretation as you would certainly know more about the CEC than I. It seems strange to me that our codes, which seem to be generally pretty harmonious, would be at odds on something as commonplace as this.
I find it odd as well especially seeing as how don_reqcapt19 posted manufactures instructions which are contrary to the CEC.

Its got me wondering now and I'm going to bring it up at the seminar next month for the new 2015 CEC.
__________________
I want to get a job cleaning mirrors......its something I can see myself doing.
Rollie73 is offline   Reply With Quote
Old 02-16-2015, 09:00 PM   #25
Very Long Vacation
 
Join Date: Jan 2011
Location: united states of america
Posts: 11,766
Rewards Points: 5,262
Default

Quote:
Originally Posted by glen1971 View Post
Always been told they are grounded at one end only to eliminate circulating sheath currents, the same way single conductors are dealt with...
[quote=Rollie73;1673473]


In MV cables with typical runs the amount of circulating current is small, at most enough to require a current carrying capacity adjustment, but nothing more than that. We are talking amperes.

Now if the cable is traveling for many, many miles, or your talking about medium to long runs (again miles) of HV and EHV underground transmission cables the shields are often transposed between phases or connected to normally open surge arrestors at one point. Though more complex and poorer from a voltage stress point, the reasoning is to cut back on hundreds if not thousands of amperes of induced circulating currents on the cable jackets which limit real current capacity (from a thermal standpoint) and create large amounts of reactive capacitive current.

Of course in HVDC this does not have to be done.
But again, outside of large utility projects its generally not a concern.
Quote:
We don't bond them at both ends In fact....its a violation of the CEC



What is the reasoning behind that? Of course Im sure the CEC is correct, but just new to me.




Quote:
Originally Posted by Jhellwig View Post
The power company uses the shield as the grounded conductor.

They do, however the shields in utility cables used as grounded conductors are designed for such. They often will have concentric wires around the shields, and cables can be ordered with a concentric neutral equivalent to the hot conductor in size for single phase circuits or a reduced 1/3 size for 3 phase circuits where 3 cables are paired together.







Quote:
Originally Posted by Rollie73 View Post
The POCO can do whatever it wants Amazing what they get away with.

I agree POCOs do some incredibly stupid and dangerous stuff (Ive seen lawn sprinklers used to cool overload transformers) but the cables POCOs use are designed with a shield that either full sized or 1/3 the size of the phase conductor.
meadow is offline   Reply With Quote
Old 02-16-2015, 09:10 PM   #26
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Nova Scotia, Canada
Posts: 5,261
Rewards Points: 286
Default

Quote:
Originally Posted by meadow View Post
What is the reasoning behind that? Of course Im sure the CEC is correct, but just new to me.
The reasoning is to eliminate the possibility of any current flow on the shielding.

I'm no longer so sure the CEC is right after reading all the other info you guys are posting here. We could be doing it wrong here

As I said though....I will pose some questions at the seminar.
__________________
I want to get a job cleaning mirrors......its something I can see myself doing.
Rollie73 is offline   Reply With Quote
The Following User Says Thank You to Rollie73 For This Useful Post:
glen1971 (02-16-2015)
Old 02-16-2015, 10:00 PM   #27
Member
 
Join Date: May 2009
Location: South Bend, IN
Posts: 98
Rewards Points: 79
Default

Directly from Okonite's website:

Grounding Shielded Cable
When installing shielded cable, metallic shielding must be solidly grounded. Where conductors are individually shielded, each must have its shielding grounded and the shielding of each conductor should be carried across every joint to assure positive continuity of a shielding from one end of the cable to the other. Where grounding conductors are part of the cable assembly, they must be connected with the shielding at both ends of the cable.
For safe and effective operation, the shielding should be grounded at each end of the cable and at each splice. For short lengths or where special bonding arrangements are used, grounding at one point only may be satisfactory.

http://okonite.com/engineering/shielding.html
Marshall175 is offline   Reply With Quote
The Following User Says Thank You to Marshall175 For This Useful Post:
Moonshot180 (02-17-2015)
Old 02-16-2015, 10:43 PM   #28
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Nova Scotia, Canada
Posts: 5,261
Rewards Points: 286
Default

Quote:
Originally Posted by Marshall175 View Post
Directly from Okonite's website:

Grounding Shielded Cable
When installing shielded cable, metallic shielding must be solidly grounded. Where conductors are individually shielded, each must have its shielding grounded and the shielding of each conductor should be carried across every joint to assure positive continuity of a shielding from one end of the cable to the other. Where grounding conductors are part of the cable assembly, they must be connected with the shielding at both ends of the cable.
For safe and effective operation, the shielding should be grounded at each end of the cable and at each splice. For short lengths or where special bonding arrangements are used, grounding at one point only may be satisfactory.

http://okonite.com/engineering/shielding.html
don_resqcapt19 already posted this info. He beat you to it.
__________________
I want to get a job cleaning mirrors......its something I can see myself doing.
Rollie73 is offline   Reply With Quote
Old 02-16-2015, 10:50 PM   #29
Member
 
Join Date: May 2009
Location: South Bend, IN
Posts: 98
Rewards Points: 79
Default

damn! can't believe i missed that....

sorry
Marshall175 is offline   Reply With Quote
Old 02-16-2015, 10:56 PM   #30
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Nova Scotia, Canada
Posts: 5,261
Rewards Points: 286
Default

Quote:
Originally Posted by Marshall175 View Post
damn! can't believe i missed that....

sorry
Sh!t happens
__________________
I want to get a job cleaning mirrors......its something I can see myself doing.
Rollie73 is offline   Reply With Quote
Old 02-16-2015, 11:02 PM   #31
Senior Member
 
Join Date: Oct 2012
Location: Alberta Rockies
Posts: 2,821
Rewards Points: 3,996
Default

Rollie - If you find out a definite answer can you please post.. I'm curious as there must be someone on the CEC that knows.. Unfortunately, the chair of Section 36 is from BC Hydro, but there are a few other members that are in other areas..

I did a bunch of googling and reading this afternoon and the consensus of the majority of the sites I found (US based) did say that both ends and each splice should be grounded.. I did find a couple manufacturer sites that said only one end.. A couple of those referenced a 2011 NEC article, but naturally I didn't save the link...
glen1971 is offline   Reply With Quote
Old 02-17-2015, 07:57 AM   #32
AKA Luketrician
 
Moonshot180's Avatar
 
Join Date: Apr 2012
Location: Chattanooga TN
Posts: 584
Rewards Points: 1,101
Default

really appreciate everyones input here, been a great read for me.

The cables in question run approx 40 feet, up to a 1750 hp hitachi synchronous motor. Supply cables run from the gear, approximately 1000 feet to a step down TX, 6.9kV to 480, to feed the exciter cabinet...from there off of H1 H2 H3, a parallel run goes up to the motor termination j/b. I know that both ends of that long run have the shields grounded at both ends.

The 40 run up to the motor is grounded at the TX side, just not at the J/B.
Moonshot180 is offline   Reply With Quote
Old 02-17-2015, 07:57 AM   #33
Senior Member
 
Join Date: Jul 2010
Location: IL
Posts: 3,838
Rewards Points: 1,224
Default

The NEC just requires that the shield be grounded, but does not specify that it be grounded at a single or multiple locations.

There is a rule in the 2011 code that says you may have to adjust the ampacity of a shielded conductor where the shielded is bonded at multiple points. This is because any current flow in the shield will produce some additional heat and that will add to the heat of the conductor itself and may require an ampacity adjustment.
Quote:
310.60(B)(1) Grounded Shields. Ampacities shown in Table 310.60(C)(69), Table 310.60(C)(70), Table 310.60(C)(81), and Table 310.60(C)(82) are for cable with shields grounded at one point only. Where shields are grounded at more than one point, ampacities shall be adjusted to take into consideration the heating due to shield currents.
don_resqcapt19 is offline   Reply With Quote
The Following 4 Users Say Thank You to don_resqcapt19 For This Useful Post:
Arc'n'Spark (02-17-2015), glen1971 (02-17-2015), Moonshot180 (02-18-2015), Rollie73 (02-17-2015)
Old 02-17-2015, 08:37 PM   #34
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Nova Scotia, Canada
Posts: 5,261
Rewards Points: 286
Default

Glen.....as soon as I find a definite answer, I will be sure to post it up here. I did speak with one inspector a bit about today and he really wasn't able to shed any light on the situation because he was primarily a residential guy before going into inspections He had actually forgotten all about shielding on MV cables.
__________________
I want to get a job cleaning mirrors......its something I can see myself doing.
Rollie73 is offline   Reply With Quote
The Following User Says Thank You to Rollie73 For This Useful Post:
glen1971 (02-17-2015)
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Low voltage, Medium Voltage 99cents General Electrical Discussion 18 08-01-2013 11:22 PM
Sanity Check MattHelm Residential Electrical Forum 2 07-05-2012 04:39 PM
Low voltage and medium voltage devices sharing same enclusure AFE NEC Code Forum 12 05-20-2012 12:25 PM
Medium Voltage T Taps Scott657 General Electrical Discussion 13 04-05-2011 06:20 PM
medium voltage burial DEA AGENT NEC Code Forum 7 05-24-2008 12:20 AM


All times are GMT -4. The time now is 03:28 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com