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The letters A and H can be found on the front face of the thermal relays and they correspond to the choice of reset type on an overload fault:
H: Manual reset
A: Automatic reset
Manual reset requires that the blue button on the front face is physically depressed to reset the overload once it has cooled down after an overload trip. This may be directly, via a plunger type "Stop" button mounted immediately in front of the overload, via a cable operated remote reset switch or by a "reset solenoid" which can remotely operated by an electrical pulse. All these are forms of "Manual" reset.
Automatic reset requires no external operation. After the required time period, which will vary according to the type and severity of the overload trip, the overload will cool down sufficiently and the trip wil reset it self. Care must be taken that a control design is not used which could lead to an unexpected re-start in situations which could pose a threat to personnel. For such safety reasons, Manual reset would be the usual choice, thereby requiring a definite intentional action to make a machine ready to run again.
LRD: Thermal relay for the LC1D contactor range
Since June 2005, all LRD01 to 38 products in the Tesys D range have had the option of reversible setting of manual or automatic reset mode
PLEASE NOTE: Prior to this date, the product was supplied in Manual mode. The LRD could be switched to automatic reset mode by a deliberate user action, removing the seal (marked H) and moving the lever down. This action was not reversible.
Since this date, the product is still supplied in Manual mode, the operation to switch to automatic reset mode is identical, but it is now reversible: the lever can be moved in both directions, and H (manual) and A (automatic) are marked on the product: front face and side label, as shown in the attached diagram
LR2K thermal relay for the LC1K contactor range
LR2K thermal relays are factory-supplied in manual reset mode.
This setting can be changed to automatic reset but this operation is irreversible.