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KT7 Front vs. Side mount Auxiliaries

Question:

What is the maximum voltage rating of KT7 front mounted auxiliary contacts verses side mounted auxiliaries. How do these differences effect KT7 assembled devices, such as E-Combo starters?

Answer:

The accessories section of our printed and e-catalog shows front mounted auxiliaries like KT7-PE1-10 are rated for 300 volts maximum. These pages also show side mounted auxiliaries like KT7-PA1-11 are rated for 600 volts AC. This means that any E-Combo control circuit above 300 volts (i.e.:380, 480, or 600 VAC) must utilize side mount auxiliary contacts (not front mounted).

Many customers use a normally open auxiliary to remove voltage from the contactor coil in case of overload, similar to terminals 95-96 of a standard overload relay. On E-Combo starters, this is not required by code since the KT7 motor circuit controller would stop passing voltage to the motor when the main contacts open under a trip condition. Still a lot of customers utilize KT7 auxiliaries in this way.

Most multi-starter control panels using KT7 would also include a control power transformer (CPT) and the control circuit would perhaps be 120 volts; then, KT7-PE1-10 is a perfect choice. Most individual E-Combo starters also include a CPT and so front mounted auxiliaries are just fine. KT7 is often used as a manual starter application where there is no contactor and no auxiliaries are required.

The introduction of the CX7 KwikStarter, where there is no room in the enclosure for a CPT, makes applications a little more challenging. When the customer provides separate control voltage (Example: 120 VAC or 24 VAC or 24 VDC) then there is no problem. Consider the possibility when someone orders a CX7-9-10-480-AS0.16A-A10-PG which our printed catalog pages seem to imply is OK. Upon closer inspection, footnotes at the bottom of the page indicate it is not OK because the 480 VAC control circuit (or 575 Volt) should not be used with a –A10 (KT7-PE1-10) auxiliary. The footnote goes on to describe that the –A10 should be changed to -AS11. This configuration, CX7-9-10-480-AS0.16A-AS11-PG utilizes the side mount 600 VAC rated auxiliaries.

This change in part number for applications above 300 VAC, from the front mounted to the side mounted auxiliaries, effects the following configuration prefixes:

• CL7 & CLU7
• CK7 & CKU7
• CLT7 & CLUT7
• CX7 & CXU7
• CXP7 & CXDP7
• KTA7 & KTU7

Although it is marked clearly in the catalog, sometimes it is possible to overlook such details in building various types of assemblies.