True RMS Earth Leakage Relay

It uses a toroid..

..." the RMS voltage (V_RMS) of a sinusoidal waveform is determined by multiplying the peak voltage value by 0.7071"...

The forum would be interested to know the outcome of telephone discussions with the equipment manufacturer, for that is where the answer to that question may be found and is the easiest way to find it.

<...25ms...>

1/40 of a second is ample time for a current to reach <...RMS...5 x greater than the set trip current...50 and 60 Hz...>.

How did the chat with the equipment manufacturer go, please?

AC reaches maximum voltage in less than 1/2 cycle. 1/2 cycle at 50Hz is 10 ms, 1/2 cycle at 60Hz is 8.33 ms. "Inst" means the relay trips as soon as overcurrent is detected. "50 ms" means if overcurrent is detected there is a built in delay.

"Definite (instantaneous)-current protection

This relay is referred as definite (instantaneous) overcurrent relay. The relay operates as soon as the current gets higher than a preset value. There is no intentional time delay set. There is always an inherent time delay of the order of a few milliseconds.

Definite-time protection

In this type, two conditions must be satisfied for operation (tripping), current must exceed the setting value and the fault must be continuous for at least a time equal to the time setting of the relay."

https://electrical-engineering-portal.com/download-center/books-and-guides/relays/overcurrent-protection-basics

The minimum time interval where both 50 and 60 Hz signals are almost synchronized is 100ms (6 cycles of 60Hz and 5 cycles of 50 Hz)

This is irrelevant. The relay can be used for 50Hz OR 60Hz, not both at the same time.

<...irrelevant...>

Incorrect, more likely.

What link?

The word Link in the original post has the link behind it.

. . . without the underlining, I had to look twice to see it. The color difference on my monitor is subtle.

In the interest of clarity, I prefer links to be their full URL or at least set it apart from the other text or at the very least use the underline.

Mine to, I couldn't clearly see on my monitor either and assumed and put the curser over it to find out.

The datasheet in your link shows the value of Inst as <25mS (not a set defined time value but a value of up to almost 25 mS or less).

...because the current could be anywhere on the sine wave at the instant of connection to the fault. GA

Thanks for the answers above. Actually, doing peak detection would offer the quickest response as one just compares to a threshold and trip. My worry actually is that I would not want to assume the waveform is pure sine. In that case a peak detection would not be reliable (I think). RMS could be more a reliable way of measuring the current if it is distorted or noisy, but I don't think one can do good RMS in less than 25 ms considering that system can't quickly identify if the signal is 50 or 60Hz in order to maybe adjust the number of samples (if it has some ADC in it).

That's not the point. The equipment isn't doing an <...RMS...> calculation over several seconds. It's tripping when the current exceeds it trip setting, and that event can happen in less than half-a-cycle. Hence the trip time claim.

<unsubscribes>

The circuitry is monitoring the leakage current continuously and once it detects a current exceeding the setpoint it will trip within the time frame set. Inst refers to instantaneous. The RMS value of the current isn't necessarily a sinusoidal current and could be caused by a load going to ground that causes the current to contain harmonics or excessive currents caused by inductive loads to ground that cause the iron/core material to saturate and cause a very distorted current waveform.