myenergi recommend that a 32A Type B MCB (or RCBO) is used to protect the circuit to the zappi EV charger
In this article:
We have thousands of zappi's installed and have received very few reports of problems with nuisance tripping when using a 32A Type B MCB
When selecting the MCB there are three factors that need to be considered:
- The expected continuous loading of the circuit,
- Derating for ambient temperature, and
- Any derating factor that needs to be applied to the MCB due to ambient temperature or the fact that the MCB's are closely packed together in the consumer unit.
1. Continuous Rating
The Time/Current curve for a Type B MCB shows that, even if continually loaded, the thermal trip will not operate unless the current is greater than 1.13xIn
So, for a 32A MCB, it should not trip unless the current is above 36.16A
2. Temperature Derating
In most installations a temperature derating for the MCB does not need to be considered, provided the ambient temperature does not exceed 30degC. The MCB manufacturer's data sheet should always be consulted, for instance, here is the temperature derating information published by Hager of their MCB's, showing that a 32A MCB only needs to be derated if the ambient temperature exceed 30 degC.
3. Packing or Grouping Factor
Where a number of MCB's are installed together then it may be appropriate to apply a derating factor. The guidance from the MCB manufacturers varies, but is based on the worst case scenario of all the MCB's operating continually at their rated capacity. In most circumstances the MCB(s) will not be operating continually at its rated value so derating factor is not significant.
Where the all the MCB's are heavily loaded then a Grouping Factor may need to be applied, for example:
In this case it may be appropriate to install a higher rated MCB.
Ultimately the responsibility for selecting the correct MCB lies with the installer based on the particular details of the installation and specifically to ensure that the cable downstream of the MCB does not overheat. As we do not know the details of every installation we need to base our recommendation on a reasonable base case. Where the installer fits a dedicated consumer unit for the zappi supply, or there is single 32A circuit in an existing consumer unit where the other loads a generally lightly loaded then a 32A Type B MCB is perfectly suitable.
In a commercial installation where a number of zappis are fed from MCBs in the same consumer unit / panel then the grouping factor will apply and a 40A MCB may be more appropriate.
Type B or Type C tripping characteristic
Some installers prefer to fit a Type C MCB to avoid nuisance tripping.
Our recommendation is that a Type B MCB is perfectly adequate.
There is no significant inrush current to either the zappi or the EV.
The EV onboard charger increases the load current gradually so should not trip the Type B MCB which will trip "instantly" on currents in the range 3-5xIn
Type C MCB's are generally used for inductive loads such as motors, and discharge lighting where there are high start-up currents, rather than power electronic converters such as those found in EV on board chargers
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