Biddle MEGGER - Page 32

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After

connecting

the

leads

to

the

instrument,

and

just

before

connecting

them

to

the

apparatus,

make

sure

there

is

no

leak

from

lead

to

lead.

Do

this

by

operating

the

instrument,

which

should

read

Infinity.

Do

not

correct

slight

lead

leakage

by

attempting

to

reset

the

Infinity

Adjuster

on

a

high

range

in-

strument.

Then

touch

the

test

ends

of

the

leads

together

to

make

sure

they

are

not

disconnected

or

broken.

Current

testing

with

the

high

range

(50,000

megohms)

Megger

insulation

testers

requires

that

the

LINE

test

lead

be

maintained

at

a

high

value

so

that

it

will

not

enter

into

the

measurement.

The

shielded

test

lead,

with

the

shield

connected

to

GUARD

prevents

any

leakages,

over

its

terminations

or

through

the

lead

insulating

material,

from

being

measured.

Instructions

For

Use

The

untagged

end

of

the

shielded

lead

is

to

be

connected

to

the

Line

and

Guard

terminals

of

the

“Megger”

instrument

—the

end

terminal

to

Line

and

the

side

(shield)

terminal

to

Guard.

The

clip

on

the

Line

lead

is

connected

to

the

apparatus

under

test

in

the

regular

way.

The

outboard

Guard

terminal

may

be

connected

to

that

part

of

the

apparatus

under

test

which

the

user

wishes

to

guard.

The

conductor

employed

in

making

this

connection

must

be

insulated

for

the

voltage

rating

of

the

“Megger”

instrument

used.

Effect

of

Capacitance

Capacitance

in

apparatus

under

test

must

be

charged

up

to

the

rated

d-c

voltage

of

the

“Megger”

Insulation

Tester,

and

maintained

for

30

to

60

seconds

before

a

final

reading

is

taken.

Make

sure

that

capacitance

is

discharged—by

short-circuiting

and

grounding

the

apparatus

before

connecting

the

test

leads.

See

Discharge

of

Capacitance,

page

1].

NOTE:

Capacitance

causes

the

pointer

to

swing

towards

Zero

while

the

“Megger”

instrument

is

being

brought

up

to

speed;

and

to

swing

off

scale

beyond

Infinity

when

the

genera-

tor

is

slowing

down.

This

is

simply

the

charge

current

flowing

into

and

out

of

the

capacitance

and

through

the

deflecting

coil

of

the

ohmmeter.

Capacitance

effects

are

most

noticeable

in

large

generators,

in

power

and

communication

cable

more

than

a

few

hundred

feet

in

length,

and

in

capacitors.

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