Yes, Ex d enclosures can be and must be joined together with a Y seal, normally a Y type explosion proof sealing fitting which have an extra dichotomous entry to pour the explosion proof seal compound to block all conduit entries. Ex d enclosures is flame proof enclosure where explosion is possible to occur inside the enclosure, a Y explosion proof seal can stop the inner explosion heat pass to the conduit through the explosion proof seal, you can also read the article "Where do you put explosion-proof seals"