Venergy Extending Current Transformer Wire Leads

7/30/2019 Venergy Extending Current Transformer Wire Leads

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International Headquarters20 Greenhill Crescent

Watford Business Park

Watford, Herts, WD18 8XG. UK

P: +44 (0)1923 495495

F: +44 (0)1923 228796

Service & Support Center

6 Green Tree Drive

South Burlington, VT 05403

P: 800-553-3879

F: 800-954-7016

North America Headquarters

203 Cooper Circle

Peachtree City, GA 30269

P: 800-553-3879

F: 800-954-7016

Application

Note

Overview

I you want to extend the current transormer wire leads, there are our basic options:

Twisted - Our standard CT leads are twisted. Twisting is important or noise immunity, espe

cially at 60Hz.

Shieldedandtwisted - Adding a shieldin addition to the twistingcan oer some addition

noise immunity, especially or long extensions. Note: or best immunity to crosstalk, the wires

should be twisted in pairs.

Non-shieldedandnon-twisted - Most cables are twisted, so this normally only arises i you

use two single conductors. We recommend against this or most applications, because there

very little noise immunity. This can work i the conductors or each CT are kept in close contac

to minimize loop area and i the CT conductors are kept away rom line (mains) conductors and

in their own conduit or metal raceway.

Shieldedbutnon-twisted - This is a bit unusual, but does occur. There are two concerns wit

this type o cable. First, the shield primarily blocks high requency intererence, but not 60Hz.

60Hz is much better blocked by twisting the wires. 60Hz intererence is a big concern, becausthere is a lot o 60Hz noise and its the main requency we are measuring. Second, because th

wires are not twisted into pairs, there is a greater risk o crosstalk between CTs i you run more

than one pair o CT wires in the same cable. I possible, use twisted pair cabling when extendi

CT wires.

Shielded

Shielded CT wires should oer some additional noise immunity, especially i the shield is connected to

earth ground at BOTH ends. Shielded cable is typically available in 300V and 600V ratings. The 300V

rating should be sufcient or 120/208/240VAC panels and circuits, but 600V rated cable should be

used or 277/480VAC and 347/600VAC panels.

I you are extending multiple CTs, it is possible to buy cables with multiple pairs to cut down on thenumber o cables to run. We recommend no more than three pairs per cable.

We recommend extending with 22, 20, 18 or 16 AWG cables. 22 AWG and 20 AWG will be the easie

to work with.

ExtendingCurrentTransformerWireLeads

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P: +44 (0)1923 495495

F: +44 (0)1923 228796


6 Green Tree Drive


P: 800-553-3879

F: 800-954-7016


203 Cooper Circle


P: 800-553-3879

F: 800-954-7016

Application

Note

ManuacturerPart

Number

Voltage

Rating

Wire Pairs/

Conductors

AWG Temperature

RangeUL / NEC Diamete

Carol C2536A.

41.10

600V 1 / 2 16

AWG-20C to

75C

UL 2106

NEC CL2

0.308

Alpha Wire 3221

SL001

600V 1 / 2 22

AWG-55C to

105C

0.181

Alpha Wire 3231

SL001

600V 1 / 2 20

AWG

-55C to

105C

0.189

Tyco / Raychem 44A1121-

22-0/9-9

600V 1 / 2 22

AWG-65C to

105C

0.132

Tyco / Raychem 44A1121-

20-0/9-9

600V 1 / 2 20

AWG-65C to

105C

0.148

Belden 9341

0101000

600V 1 / 2 18

AWG-30C to

90C

UL 1277

NEC TC

0.276

Belden 9841 300V 1 / 2 24

AWG-30C to

80C

UL 2919

NEC CM

0.232

Alpha Wire 6010C

SL005

300V 3 / 6 22

AWG-20C to

60C

UL 2493 0.310

Alpha Wire 6456

BK005

300V 3 / 6 22

AWG?? 0.414

Belden 9369-500-60 300V 3 / 6 18AWG -30C to105CUL 2493NEC CM

0.298

Belden 9553-

1000-60

300V 3 / 6 18

AWG105C UL

NEC

0.411

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ShieldedCableManufacturers


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P: +44 (0)1923 495495

F: +44 (0)1923 228796


6 Green Tree Drive


P: 800-553-3879

F: 800-954-7016


203 Cooper Circle


P: 800-553-3879

F: 800-954-7016

Application

Note

Unshielded

The standard CT wires are unshielded, but have good noise rejection due to the twisting o the wires.Unortunately, these wires are not available as a stock item and must be custom ordered.

Supplier: Allied Wire

Web: http://www.awcwire.com

Phone: (800)828-9473

Part#: UL-1015 22GA BLK&WHT CUSTOM BULK WIRE - 1 TWIST.

Alternates

These unshielded cables should be more readily available.

Manuacturer Part

Number

Voltage

Rating

Wire

Pairs/Conduc-

tors

AWG Temperature

Range

UL / NEC Diameter

Belden 9486

0101000

600V 1 / 2 18

AWG-30C to

90C

UL 1277

NEC TC

0.275

Splicing

When extending the CT wires, you will need to splice the existing wires to the extra wire or cable.

You may want to shorten the original CT wires, especially i you are going to use shielded

cable and ground the shield to earth ground.

Avoid creating large loops or gaps between the white and black wires at the junction point,

because this can increase electrical intererence.

I possible, a soldered connection with heat shrink tubing provides the most proessional

connection, but this is more time consuming.

The next recommendation is an inline crimp connection. There are several systems or joining

wires this way that work well.

We recommend against using wire-nuts to extend the CT wires. Wire nuts dont hold well or

22 AWG stranded wire and it is difcult to keep the wires parallel and close to each other.

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P: +44 (0)1923 495495

F: +44 (0)1923 228796


6 Green Tree Drive


P: 800-553-3879

F: 800-954-7016


203 Cooper Circle


P: 800-553-3879

F: 800-954-7016

Application

Note

SignalAttenuation

Long lengths o cable can slightly attenuate the CT signals (in addition to increasing susceptibility tonoise). The ollowing table shows the required total CT length to reduce the CT signal by 0.1% as a

unction o AWG, based on the Power Meter CT input resistance o 23 kilo-ohms.

AWG Ohms / 1000t Cable Length or

0.1% Attenuation

16 4.016 2850

18 6.385 1800

20 10.15 1130

22 16.14 710

24 25.67 450

EffectofInterferenceorCrosstalk

Customers commonly ask how much error will be introduced by extending the CT leads or by using

dierent types o cables. Unortunately, there is no quantitative answer to these questions.

In the case o crosstalk, the amount o crosstalk depends on the ollowing:

Signal requencies: i your load has strong harmonics, there could be more crosstalk.

Cable properties: such as the capacitive and inductive coupling between adjacent conductors

CT source impedance: dierent current transormers have dierent winding resistances and

internal burden resistors, resulting in dierent source impedances and dierent susceptibilities

intererence and crosstalk.

Cable length: the longer the cable, the more crosstalk.

Signals on dierent CTs: are you monitoring a balanced three-phase load or are there complet

dierent current signals on dierent CT cables?

Many o these variables are unknown and their interactions with each other are difcult to predict. Wit

the recommended cable types (twisted pair, optionally shielded), crosstalk should be neglible. With

other cables, it is impossible to predict i crosstalk will signifcantly aect the accuracy.

Intererence is also impossible to accurately predict or quantiy, because it depends on all the actors

or crosstalk, as well as the amplitude and requency o the intererence, the distance rom the source

o the intererence, and external shielding, such as conduit.

In our experience, it is easier to avoid long CT lead extensions and i you must extend the leads, to us

good cables.

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Venergy Extending Current Transformer Wire Leads