Making An Rcd Measurement; Selecting Rcd Type - Megger MFT1800 Series User Manual

Residual Current Device (RCD) or Ground Fault Current Interrupt (GFCI) testing
The characteristics of each RCD type is detailed below:
RCD Type AC
Operate with AC
residual earth currents
Description
only.
Symbol used
Application
Trip times
½ I
1 x I
2 x I
5 x I
8.1

Making an RCD measurement

NOTE :
„ To select 0º or 180º press and release the mode button
(Note: Type B is not available on MFT1815 instruments)
10 mA and 30 mA RCD's should be tested at ½ x I, 1 x I and 5 x I
„
All other RCDs only need to be tested at 1 x I
„
„ I = trip current rating of the RCD
„ 2 x I available on the MFT1825 and 1835 only.
„ Connecting the neutral test lead in either of the above options will not affect the RCD but will detect a reverse
polarity and, the testing will be inhibited.
8.2

Selecting RCD type

Using the right hand (secondary range knob) select the RCD trip rating.
This is printed on the RCD (10 mA, 30 mA 100 mA etc.)
Select the RCD type, either AC, A, S or B by pressing and HOLDING DOWN the mode button
whilst in RCD test mode. Repeat until the RCD type is displayed. Refer to table above for symbol options and
descriptions.
NOTE : Type B RCD testing is NOT available on MFT1815.
38 MFT1800 series
A
Operate with AC and
pulsed DC residual
earth currents.
General purpose Protects against
protection of AC and pulsed DC
Sinusoidal AC (rectified AC).
supplies.
Trip times as defined in BS EN
>300 ms >300 ms
(>1999 ms UK) No (>1999 ms UK)
trip No trip
≤300 ms
≤300 ms
≤150ms ≤150ms
≤40 ms ≤40 ms
(30 mA RCD's only) (30 mA RCD's only)
S
Selective RCD
Operates on type AC
with time delay or
type A with time delay
S
also
S
For use upstream
of a standard AC
RCD to prevent trip
contention.
ie. Allows local trip
to operate first.
TIP: Remember "S"
for "Slow tripping"
300 ms
(>1999 ms UK)
No trip
130 ms to 500 ms
60ms to 200ms
≤40 ms <150 ms
(30 mA RCD's only)
whilst in RCD test mode
B
Operate with AC
Special applications
where protection of
DC, as well as AC
earth faults may be
encountered.
Other types will not
operate on DC fault
currents.
>300 ms
(>1999 ms UK)
No trip
≤300 ms
≤40 ms <150 ms
(30 mA RCD's only)
for 2 seconds
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