The average energy company has a dividend yield of around 3.1% today. Enbridge's (ENB 1.26%) dividend yield is materially higher at 5.8%. Should investors be worried that the high yield isn't sustainable?One positive sign is the fact that the North American midstream giant has increased its dividend annually for 30 consecutive years. But that alone doesn't mean the dividend is safe.What does Enbridge do?The energy sector is usually broken down into three broad groups. The upstream (energy production) and th ...