The table below summarises the plug types, voltage and frequency of electrical current in both Eritrea and Tonga.
|Frequency of electrical current||50Hz||50Hz|
Eritrea uses Plug Type C.
You will need this adaptor:
Socket Type C
(Eritrea) to Plug Type I
The voltages found in Eritrea (230V) and Tonga (240V) are not exactly the same, but the difference is tolerable, so you should not need a transformer.
The frequency found in Eritrea and Tonga is exactly the same (50Hz). Timing devices and appliances that use motors will function as expected under this frequency.