Two-Phase & Three-Phase
Solid State Relays & Power Controllers
Frequently asked questions
What is meant by “Multiphase” power controller?
Multiphase power controllers, such as two-phase and three-phase power controllers, are designed to switch power to three-phase loads. Depending upon the configuration of the controller, either two or three legs of the load can be switched. Some multiphase controllers utilize two or three 50 amp, 90 amp or 125 amp single-phase solid-state relays to control the load, while others might use one 50 amp per-phase three-phase solid-state relay to perform the same function.
Can I use three-phase power controllers/ multi phase controllers to switch single-phase AC loads?
Yes. This is not uncommon in applications where multiple loads need to be switched from within a single control panel. For example, the HBC-90HDG-3 is rated to 50 amps per-phase and utilizes three 90 amp solid-state relays, which could be used to switch power to a three-phase load. However, it could also be used to switch 50 amps to three separate single-phase loads. Since the three solid-state relays are independent from one another, they can be controlled by separate input signals.
The HBC-T50xK is also a type of multiphase power controllers but utilizes a single three-phase SSR. The outputs are also independent from each other and could potentially be connected to three separate loads. However, unlike the HBC-90HDG-3 that uses three independent solid-state relays, the three-phase solid-state relay has a common input. Therefore, when an input signal is applied to the solid-state relay, all three outputs will turn on and conduct load current simultaneously.
What type of solid-state relays are used on multiphase power controllers?
Multiphase power controllers either use multiple AC output single-phase solid-state relays, or one three-phase solid-state relay. Both are SCR-based solid-state relays, and both perform the same function. That is, regardless of the solid-state relay configuration used, they’re designed to switch power to/from a three-phase load. The primary difference is in how they’re wired within the panel. If the power controller utilizes two or three independent solid-state relays, then the input terminals of each solid-state relay are typically wired in parallel so that they turn on simultaneously when the control signal is applied. However, power controllers that utilize a three-phase solid state relay, such as the HBC-T50xK series, share a common input. When the control signal is applied to that version, all three outputs turn-on simultaneously.
Is there a DIN or panel-mount option for each multiphase solid state power controller?
Most power controllers have an option for either DIN or panel mounting. Three-phase power controllers that utilize S, A, L or K series heat sinks are DIN mount by default but have an option for panel mounting. The N, G, F and F7 series heat sinks are panel mount, by default. Due to the overall assembly weight, only the N series controllers have an option for DIN mounting.
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What is the difference between two-phase and three-phase solid-state power controllers?
The primary difference between two-phase and three-phase power controllers is the number of solid-state relays used in each design. Both are used to switch power to three-phase loads, but the manner in which they do so is slightly different. Three-phase power controllers either have 3 independent solid-state relays or 1 three-phase solid-state relay. The output of each solid-state relay is connected between one of the three phases of the three-phase network and the load being controlled, such as a resistive heating element. If the power controller uses three independent solid-state relays, then the input terminals of those relays are typically wired in parallel. Therefore, one input signal will control all three solid-state relays and energize / de-energize the three-phase load simultaneously. If the power controller uses a three-phase solid-state relay, then there is only one input available, which simultaneously controls all three outputs of the SSR.
Two-phase power controllers operate in the same manner as three-phase power controllers, but only two of the three phases are wired to the solid-state relays. The third phase of the AC mains is wired directly to the load. This is the preferred configuration since there is one less solid-state relay used in the assembly, which reduces overall power dissipation by 33%. The allows for either higher current ratings for the power controller, or the use of a smaller power controller to conserve space in the panel. Accordingly, two-phase power controllers are also slightly less expensive than their three-phase counterparts.
One important note with regard to two-phase power controllers; they work well with three-phase loads in Delta configuration, or in Wye configuration without a neutral connection. However, a three-phase controller must be used if the load is in Wye configuration with a neutral connection. Otherwise, the load connected directly to the AC mains would be on continuously.