Dwyer Zener Barrier Models MTL7706/7787

The MTL7706/7787 is an intrinsically safe (IS) shunt-diode barrier that can be used to communicate with and provide isolations for certain Dwyer® transmitters approved for use in hazardous areas.

Compatible Models: 637, 638, 639, 608, 2200

MTL Zener Barrier	Approval	Dwyer Series
MTL7706	FM for Class I, II, II; Div. 1 Groups C, D, F, G	638
MTL7706	UL for Class I, II, III; Div. 1 & 2 Groups C, D, E, F, G	639
MTL7706	FM for Class I, II, III; Div. 1 Groups B, C, D, E, F, G	637
MTL7706	FM for Class I, II, III; Div. 1 Groups A, B, C, D, E, F, G	608
MTL7787	FM for Class I, II, III; Div. 1 Groups A, B, C, D, E, F, G	2200

MTL7706	FM
	Group	μF	mH
	A & B	0.083	4.2
	BASEEFA (ATEX0)
	Group	μF	mH
	IIC	0.083	4.2

MTL7787	FM
	Group	μF	mH
	A & B	0.083	4.2
	BASEEFA (ATEX0)
	Group	μF	mH
	IIC	0.083	4.2

Region (Authority)	Standard	Approved For	Certificate/file no.
USA (FM)	3600, 3610 entity 3611, 3810	AIS/I,II,III/1/Entity ABCDEFG-SCI-942; NI/I/@/ABCD/T4 [I/0] AEx[ia]IIC-SCI-942 Entity; NI/1/2/IIC/T4; Ta=140°F (60°C)	3010737
Canada (CSA)	CAN/CSA E60070, UL698, UL913, UL1604, IEC60079, C22.2	Class I, Div.2, Gps A, B, C, D; Ex nA [iA] IIC T4 Class I, Xone 2, Aex nA IIC T4	1345550
UK (BASEEFA)	EN 50014, EN 50020	EEx ia IIC	BAS01ATEX7217
UK (BASEEFA) Systems	EN 50039	EEx ia IIC	Ex01E2219

A Little Bit About Using Zener Barriers and Galvanic Isolators

The MTL5041/5045 Galvanic Isolators provide total intrinsically safe isolation for communication with Dwyer® pressure transmitters approved for location in hazardous areas. Galvanic isolation eliminates the need for a high integrity earth ground required when using shunt diode type safety barriers. DIN rail mounting and plug-in signal and power connectors simplify installation and maintenance.

Compatible Models: 637, 638, 639, 608, 2200, 2900

The MTL7706/7787 is an intrinsically safe (IS) shunt-diode barrier that can be used to communicate with and provide isolations for certain Dwyer® transmitters approved for use in hazardous areas. These barriers limit the amount of energy allowed to pass into the hazardous area, which inhibit ignition in flammable atmospheres. Requires high integrity earth ground

Compatible Models: 637, 638, 639, 608, 2200

What is a Good ground resistance value?

There is a good deal of confusion as to what constitutes a good ground and what the ground resistance value needs to be. Ideally a ground should be of zero ohms resistance.

There is not one standard ground resistance threshold that is recognized by all agencies. However, the NFPA and IEEE have recommended a ground resistance value of 5.0 ohms or less.

The NEC has stated to “Make sure that system impedance to ground is less than 25 ohms specified in NEC 250.56. In facilities with sensitive equipment it should be 5.0 ohms or less.”

The goal in ground resistance is to achieve the lowest ground resistance value possible that makes sense economically and physically.