17/12/97
Page 32
Issue H
10.8 Housing
Throughout the MR series range a modular housing system has been employed, utilising the latest
high quality UK manufactured industry standard case components. This approach affords maximum
flexibility for both the relay scheme designer and the maintenance engineer. The relay modules are
fully Withdrawable for ease of maintenance and where applicable incorporate automatic short-
circuiting CT connections to avoid dangerous open circuit CT overvoltages. A clear plastic front
cover is provided for inspection purposes. A push button allows re-setting of the relay following a
trip and also interrogation in display mode (1) without having to open the cover.
MPR 3E5
units are supplied in standard height (179mm
≅
7in.) cases, complying with IEC 297 size 4U.
The rigid case wall is manufactured from a single sheet of hot dipped galvanised steel coated
externally with Plastisol PVC and internally with a low gloss alkyd paint finish. This construction
technique provides improved thermal transfer characteristics over plastic walled cases and combines
exceptional corrosion and flame resilience with good electromagnetic and electrostatic screening
properties allowing many relays to be freely situated in close proximity and hazardous environments.
When the relay is inserted a leaf spring along the top edge of the module makes contact with a
solidly bonded nickel plated steel strip on the interior of the case, providing excellent earth
continuity. This strip is brought out at the rear of the case, above the terminal block, where it forms a
separate earthing terminal. A rigid front mounting flange is provided allowing the entire range of
standard cases to be flush mounted without alteration. These flanges are also used to mount the relay
inspection cover which is secured by thumbscrews. Securely bonded channels can be provided on the
top and bottom surfaces toward the rear of the case allowing large rigid assemblies to be created by
the use of joining strips located in these channels.
This uniform but highly flexible housing system integrates excellent mechanical strength with good
electrical practice in industry standard sizes.
PANEL CUT OUT FLUSH
MOUNTING FIXING DETAILS
4 HOLES 4.4mm DIAMETER
99
168
159
52
23.5
10
97
45
PUSH BUTTON
PROJECTION 10mm
NOT SHOWN TO SCALE
103
177
212
Clearance
25 min
157
32
OPTIONAL
OPTIONAL
OPTIONAL
Min
28
NOTE Minimum gap between vertical
spacing is required in order to
withdraw relay from the case above.
178
Required to open case
SIZE 100 CASE
