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Solid State Relays for single phase and three-phase resistive loads (AC-51)
Heating applications with regulation need a high frequency ON/OFF.
Zero cross Solid State Relays are perfect for such an application.
When choosing an SSR, mains voltage, heating power, but also the heating element value in cold conditions must be taken into account.
Single Phase Resistive Load
Definition of a switching current
In cold and hot conditions there is a significant difference in values between some types of heating elements.
For example, some constantan nickel-chrome heating elements can have an inrush current in cold conditions = 1.4 times the nominal current.
Standards for AC-51 loads state that a starting current in cold conditions must = 1.4 x the nominal current.
Generally speaking, oversizing the current and heatsink relay can improve thermal fatigue.
I = P/U
Current (A) =
Power Load (W) / Mains voltage (V)
Single phase Solid State Relays (SSR) for resistive loads
Our SO9 range is perfect for this type of application. These are on-off, zero cross relays.
Please note that for heating elements with wire-wound resistors, the switching current may be up to 1.4 times the assigned current.
Power SSRs with Diagnostics Features
At the end of a heating element’s service life, the load is generally open. Our SOD range can detect this problem.
These relays let the user know the actual status of the load (resistive load), the output of the relay and the network via an NC (Normally Closed) diagnostic contact.
Full wave pulse controller
Our SG5 range consists of full wave pulse controllers. What are this control mode's operating principles?
During a given cycle (this varies depending on the respective model), the load power varies by eliminating whole alternations.
This elimination is done linearly following the cyclic Ton/Tcycle report requested by the control input.
The advantage of this type of control is that it doesn’t generate any interference because its start-up voltage is almost 0.
Three-phase resistive loads controlled by x2 single phase Solid State Relays
Definition of a switching current
For these three-phase resistive loads controlled by x2 single phase Solid State Relays (SSRs), the switching current is calculated as follows:
I = P/(Ux1,732)
Current (A) =
Power Load (W) / (Mains voltage x square root of 3)
Three-phase resistive loads controlled by x1 two-phase Solid State Relay
Definition of a switching current
For these three-phase resistive loads controlled by x1 two-phase Solid State Relay (SSR), the switching current is calculated as follows:
I = P/(Ux1,732)
Current (A) =
Power Load (W) / (Mains voltage x square root of 3)
Two-phase Solid State Relays for AC-51 resistive loads
Our two-phase range consists of two solid state relays in a standard compact 45 mm enclosure.
They are ideal for three-phase applications, only breaking two phases.
NEW - 2 leg three-phase SSRs
The SMB and SGB ranges have been designed to control three-phase loads in a delta connection or, if balanced, in a star connection without neutral. Two of the three phases are switched by
the SSR, the third is directly connected.
Three-phase resistive loads controlled by x1 three-phase Solid State Relay
Definition of a switching current
For these three-phase resistive loads controlled by x1 three-phase Solid State Relay (SSR), the switching current is calculated as follows:
I = P/(Ux1,732)
Current (A) =
Power Load (W) / (Mains voltage x square root of 3)
Three-phase Solid State Relays for AC-51 resistive loads
We offer additional solid state relay ranges for controlling three-phase loads.
A number of models are available, with ratings of up to 125 amps per phase, with either an AC or DC
input voltage.
Three-phase cel3pac® range of SSRs
The SGT9 model in the cel3pac® range has been specifically designed to handle resistive loads.
The SGT9 is available with a screw connection or with spring terminals.
Three-phase SSR cel3pac® - "Ready to use" version with integrated heatsink
In our range we have "ready to use" contactors, mounted on heatsinks.
Three-phase sightpac® SSR
The sightpac® SMT9 range is ideal for AC-51 resistive loads and is housed in a standard compact 45 mm enclosure.
Three-phase sightpac® SSR - "Ready to use" version with integrated heatsink
Our 45mm compact three-phase SSR is also available mounted on a heatsink.