Frequently asked questions

FA124617

30 September 2021

Issue:
Identifying trip point in a single phase sensitive overload relay

Product Line:
NEMA combination starters

Environment:
Products sold and used in the United States

Cause:
Identifying the trip point in a single phase sensitive Tesys D overload relay

Resolution:
The phase loss sensitive overloads are designed to conform to IEC standard 60947-4-1. In that standard is this paragraph:

8.2.1.5.2 Limits of operation of three-pole thermal overload relays
energized on two poles
With reference to table 4:
The overload relay or starter shall be tested in its enclosure if normally fitted. With the relay
energized on three poles, at A times the current setting, tripping shall not occur in less than
2 h, starting from the cold state, at the value of the ambient air temperature stated in table 4.
(Table 4 `A` multiple of current setting states 2 poles at 1.0 times the current setting, the third pole at 0.9)

Moreover, when the value of the current flowing in two poles (in phase loss sensitive relays,
those carrying the higher current) is increased to B times the current setting, and the third
pole de-energized, tripping shall occur in less than 2 h. (Table 4 `B` multiple of current setting is 2 poles
at 1.15 current setting, third pole at 0.0.)

The values shall apply to all combinations of poles.

In the case of thermal overload relays having an adjustable current setting, the characteristics
shall apply both when the relay is carrying the current associated with the maximum setting
and when the relay is carrying the current associated with the minimum setting.