Author Topic: Distances (CT wires, Spyder to MTU cable)  (Read 3316 times)

eugenie4u

  • Newbie
  • *
  • Posts: 2
  • Karma: +0/-0
Distances (CT wires, Spyder to MTU cable)
« on: February 10, 2015, 07:10:32 PM »
I have an HVAC room with 4x 5-ton 3 phase units and a smaller room directly below with 1x 10-ton 3 phase unit.

I plan on using a TED PRO LITE or a TED PRO 400 Package with one Spyder.

Clearly I can use the CT's off the Spyder to measure the 4x 3 phase units, and since the load is balanced I should be able to use a single CT per unit.

However the 10-ton 3-phase unit is located in the room directly below about 10 ft away and has a home run to the utility meter and its own small breaker box.

The options I can think of are:

A) Extend the CT cables from the Spyder to drop down into the small breaker box for the 10-ton 3 phase unit below

B) Extend the CT cables from the MTU to drop down into the small breaker box for the 10-ton 3 phase unit below

C) Place the MTU near the 10-ton 3 phase unit.

However:

1) I do not know the maximum length the CT cables can be extended for the Spyder or for the MTU.

2) I don't see in any of the literature what the length of the data cable between the Spyder and the MTU is and if there is longer version or if it can be extended?
« Last Edit: February 10, 2015, 08:57:35 PM by eugenie4u »

Support 4

  • Newbie
  • *
  • Posts: 12
  • Karma: +0/-0
Re: Distances (CT wires, Spyder to MTU cable)
« Reply #1 on: February 11, 2015, 11:19:22 PM »
The cable running between the MTU and Spyder is 1 meter in length.   The CT extensions are 80 inches (2 meters).  You can put more than one extension on the CT.

Edit- to update 
« Last Edit: February 23, 2015, 10:40:12 PM by Support 4 »

eugenie4u

  • Newbie
  • *
  • Posts: 2
  • Karma: +0/-0
Re: Distances (CT wires, Spyder to MTU cable)
« Reply #2 on: February 12, 2015, 06:36:07 PM »
Thinking in terms of electrical engineering, the CT leads should be extendable, with the maximum extension determined by

CT burden rating - instrumentation burden - CT lead burden = 0

https://www.ohiosemitronics.com/Data/PDF/Tech_Papers/TechBulletin133-HowtoDetermineMaximumCTLeadLength.pdf




This means the CT lead maximum distance is a function of the CT burden rating (i.e. burden capacity) versus the instrumentation burden on the CT AND the burden on the CT from the leads which is determined by the Secondary Current Rating, the length of the leads, and the resistance determined by the lead wire diameter (assume the extension is in a non-noisy environment or is twisted pair or shielded as dictated by the environment).


But..... there are no published specs on the CT burden rating and the Secondary Current Rating I can find for the range of CT's sold by TED, nor the instrumentation burden of the Spyder or TED Pro Lite/Pro MTU,.



The CT lead wire is 22 AWG, so the Lead Burden for 22 AWG Wire is P=I^2*R = (CT Secondary Rating)^2*(0.053 Ohms/meter)



So the answer is CT Burden Rating (VA) - Instrumentation Burden (VA) - CT Lead Burden (VA) =  CT Burden Rating - Instrumentation Burden in VA - (CT Secondary Current Rating)^2*(0.053 Ohms/meter) * (CT lead length)= 0

However, one needs the CT Burden Ratings and CT Secondary Ratings for the 20A, 60A, and 200A CT's, as well as the Instrumentation Burdens of the Spyder, and Ted Pro Lite MTU, Ted Pro MTU to solve for the CT lead length maximum.

This post (http://www.theenergydetectiveforums.com/index.php/topic,499.msg2619.html#msg2619) from 4 years ago regarding the TED 5000 MTU showed that the CT leads should be easily extendable by 100 feet for the TED 5000 MTU with the 200A CT...

To solve for the new line of equipment I need those relevant specs (CT Burden Rating in VA and CT Secondary Rating for each CT, and the Instrumentation Burden Rating in VA for each MTU and the Spyder)


Can an engineer from TED chime in or someone who has calculated those specs?
« Last Edit: February 12, 2015, 08:25:44 PM by eugenie4u »

Support 4

  • Newbie
  • *
  • Posts: 12
  • Karma: +0/-0
Re: Distances (CT wires, Spyder to MTU cable)
« Reply #3 on: February 23, 2015, 10:42:49 PM »
I went out to test this for myself. I had 12 CT extensions and no negative effects!

benjatelcom

  • Newbie
  • *
  • Posts: 10
  • Karma: +0/-0
Re: Distances (CT wires, Spyder to MTU cable)
« Reply #4 on: March 20, 2016, 10:15:01 PM »
Any idea what the burden resistor value is in the 200A TED5000 CTs?